Smartwatches / Compare

Fitbit Sense 2 vs Xiaomi Watch S4

A

Product A: Fitbit

Sense 2

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B

Product B: Xiaomi

Watch S4

83 of 150 known

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Only differences

AFitbit Sense 2

BXiaomi Watch S4

General

7 of 10 differ

Series

Sense4Press releaseblog.google/products-and-platforms/devices/fitbit/versa-4-sense-2Read 23 October 2026Fitbit names the product Sense 2 in its Sense line and calls it its most advanced health-focused smartwatch.

Watch S3Maker product pagemi.com/global/support/faq/details/KA-517264Read 15 October 2026Q4 compares the Watch S4 with its predecessor, the Xiaomi Watch S3, in the same Watch S line.

Model numbersiMaker identifiers for this exact model and its listed variants. Excludes sibling models and other generations.

FB521, FB521BKGB-US, FB521SRWT-US, FB521GLBM-US1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Regulatory notices name Model FB521 with FCC ID XRAFB521. The retail colour model numbers come from the Abt listings.19Retailer pageabt.com/Fitbit-Sense-2-Graphite-Aluminum-Shadow-Grey-Strap-Advanced-Health-Fitness-Smartwatch-24mm-FB521BKGBUS/p/182315.htmlRead 23 October 2026Abt lists manufacturer model FB521BKGB-US. FB521SRWT-US and FB521GLBM-US are on the sister Abt listings. FB521 is the model in the manual.

M2425W1, BHR9195GL, BHR9197GL, BHR9199GL4Maker spec sheet (PDF)i02.appmifile.com/229_operatorx_operatorx_xm/29/08/2026/0506b1d933bea38854867532d7b1e253.pdfRead 15 October 2026EU Declaration of Conformity for radio equipment model M2425W1, Smart Watch, listed on Xiaomi's declaration page as Xiaomi Watch S4. The 41 mm Watch S4 is M2502W1 and is a separate product. The standards list covers Bluetooth, NFC and GNSS and has no cellular standard.6Maker product pagemi.com/global/service/support/declaration.htmlRead 15 October 2026Declaration page lists Xiaomi Watch S4 M2425W1 with EU DoC and PSTI documents, separate from Watch S4 41mm M2502W1.7Spec databasegsmarena.com/xiaomi_watch_s4-13476.phpRead 15 October 2026Spec page lists models M2424W1 and M2425W1. Only M2425W1 is documented for the global model, so M2424W1 is not stored.11Retailer pageeuronics.ee/en/phones/watches/smart-watches/bhr9195gl/xiaomi-watch-s4-black-smart-watchRead 15 October 2026Retailer product code BHR9195GL for the black Xiaomi Watch S4, 44.5 g, 486 mAh, Bluetooth 5.3, 4G No.13Retailer pagepood.datafox.ee/xiaomi-watch-s4-rainbow-smart-watchRead 15 October 2026Rainbow product code BHR9199GL.14Retailer pageachatmoinscher.com/comparateur-de-prix-Montre-connectee-sportive/montre-intelligente-xiaomi-s4-bhr9197gl-gris-argente-6941812707432.htmlRead 15 October 2026Silver product code BHR9197GL.

GTIN / EAN

810073611429, 810073611443, 81007361143619Retailer pageabt.com/Fitbit-Sense-2-Graphite-Aluminum-Shadow-Grey-Strap-Advanced-Health-Fitness-Smartwatch-24mm-FB521BKGBUS/p/182315.htmlRead 23 October 2026Abt lists FB521BKGB-US with UPC 810073611429 (Graphite Aluminum with Shadow Grey band).

6941812732403, 6941812707432, 694181271166812Retailer pagepood.datafox.ee/xiaomi-s4-smartwatch-blackRead 15 October 2026Black BHR9195GL, EAN 6941812732403.13Retailer pagepood.datafox.ee/xiaomi-watch-s4-rainbow-smart-watchRead 15 October 2026Rainbow BHR9199GL, EAN 6941812711668.14Retailer pageachatmoinscher.com/comparateur-de-prix-Montre-connectee-sportive/montre-intelligente-xiaomi-s4-bhr9197gl-gris-argente-6941812707432.htmlRead 15 October 2026Silver BHR9197GL, EAN 6941812707432.

AnnouncediThe maker's first announcement of this model. This is separate from first retail availability.

24 August 20224Press releaseblog.google/products-and-platforms/devices/fitbit/versa-4-sense-2Read 23 October 2026Blog post dated Aug 24, 2022. Pre-orders started that day with worldwide availability that fall.

29 October 20247Spec databasegsmarena.com/xiaomi_watch_s4-13476.phpRead 15 October 2026Spec page: announced and released 29 October 2024 in China. The global model followed in March 2025.

Status

Available2Maker product pagestore.google.com/us/product/fitbit_sense_2_specsRead 23 October 2026The Google Store sells Sense 2 at 249.95 USD on the access date. That is a current price, not the launch price.

Available2Maker product pagemi.com/global/product/xiaomi-watch-s4Read 15 October 2026The global product page is live with specs and a buy link. GSMArena lists it as available.

PredecessoriThe model this one directly replaced, in the same line, tier and size, as the maker or a trusted review names it.

Not available

Not available

SuccessoriThe model that directly replaced this one, in the same line, tier and size. A revision such as a Slim or OLED model does not count when a next generation exists.

Not available

Xiaomi Watch S5 46mm15Reviewgsmarena.com/xiaomi_unveils_smart_band_10_pro_buds_6_sound_play_speaker-news-73032.phpRead 23 October 2026GSMArena says the Xiaomi Watch S5 comes as the successor to the Watch S4.

Launch price (US)iThe maker's US launch MSRP for the stated configuration, excluding tax. Current store prices and later discounts do not qualify.

$299.954Press releaseblog.google/products-and-platforms/devices/fitbit/versa-4-sense-2Read 23 October 2026Versa 4 is available for $229.95 and Sense 2 is available for $299.95 (USD). US prices exclude sales tax.

Not available

Launch price (EU)iThe maker's euro launch price for the stated configuration, including VAT as published. Current store prices and later discounts do not qualify.

€299.9514Spec databasenextpit.de/smartwatches/google-fitbit-sense-2Read 23 October 2026UVP 299,95 EUR, marketed from September 2022.15Press articlepcwelt.de/article/1206707/fitbit-sense-2-vorgestellt-hier-finden-sie-alle-infos.htmlRead 23 October 2026PC-Welt (Germany) at the launch: Die Fitbit Sense 2 kostet 299,95 Euro. German prices include VAT. Tech Advisor states EUR 299.95, GBP 269.99 and USD 299.95.

€159.9910Press articlefonearena.com/blog/447624/xiaomi-buds-5-pro-watch-s4-electric-scooter-5-max-price-global.htmlRead 15 October 2026Price 159.99 euros for the Watch S4. The article lists no colours and gives no tax treatment. Retail listings put the Rainbow edition at 169.99 euros, which is not a launch price and is not stored.

MarketsiISO country or region codes where this exact model or variant is sold. A source page's language does not establish availability.

US, GB, DE, AU2Maker product pagestore.google.com/us/product/fitbit_sense_2_specsRead 23 October 2026US, GB, DE and AU Google Stores offer the model with a Buy button. Current prices are not launch prices.

EU10Press articlefonearena.com/blog/447624/xiaomi-buds-5-pro-watch-s4-electric-scooter-5-max-price-global.htmlRead 15 October 2026Euro price from European announcement coverage. The global launch was at MWC 2025.

ColoursiThe maker's own colour names

Shadow Grey / Graphite Aluminum, Lunar White / Platinum Aluminum, Blue Mist / Soft Gold Aluminum2Maker product pagestore.google.com/us/product/fitbit_sense_2_specsRead 23 October 2026Colors: Shadow Grey / Graphite Aluminum, Lunar White / Platinum Aluminum, Blue Mist / Soft Gold Aluminum.

Black, Silver, Rainbow1Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 2026Silver, Rainbow and Black.

Segment

Smartwatch2Maker product pagestore.google.com/us/product/fitbit_sense_2_specsRead 23 October 2026Page title: Fitbit Sense 2 Smartwatch. The Aug 24, 2022 Fitbit blog calls it a health-focused smartwatch.

Smartwatch2Maker product pagemi.com/global/product/xiaomi-watch-s4Read 15 October 2026The page sits under Wearables as the Xiaomi Watch S4 smartwatch with a rotating crown and 150+ sports modes.

OS updates promisediYears of explicitly promised OS updates. A security-only support period does not establish an OS-upgrade promise.

Not available

Not available

Security updates untiliExact end date published for security-update support of this model. Do not calculate it from a stated number of years. A security-only period does not promise OS upgrades.

Not available

2 March 20275Maker spec sheet (PDF)i02.appmifile.com/791_operatorx_operatorx_xm/05/03/2026/e12c7be544083cc45f26f933fa49ae28.pdfRead 15 October 2026UK PSTI statement for M2425W1 dated 2025/2/6: the defined support period is until 3/2/2027. Xiaomi's other PSTI statements use month/day/year, such as 11/15/2026 and 2/27/2028, so this reads as 2 March 2027. This is a security-support period, not an OS-upgrade promise.

Case

5 of 8 differ

Case sizeiMarketed case-size options. The marketed size can differ from physical case height, such as ceramic editions. Base dimensions describe the smallest base-material case.

Not available

47.3mm1Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 2026The maker states 47.3 mm x 47.3 mm x 12.0 mm. The separate 41 mm Watch S4 has its own page and is not included.

Case shape

Rectangular14Spec databasenextpit.de/smartwatches/google-fitbit-sense-2Read 23 October 2026Gehäuseform: eckig (square).

Round3Maker product pagemi.com/global/support/faq/details/KA-517264Read 15 October 2026Q2: round AMOLED display and 47.3 mm diameter.

Case materialiMaterial of the housing body, not just the bezel. Use Mixed when the maker describes a mixture of housing/frame materials. Read the published-material field for the parts and proportions.

Aluminium1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Materials: the housing and buckle on Sense 2 are made of aluminum.14Spec databasenextpit.de/smartwatches/google-fitbit-sense-2Read 23 October 2026Gehäusematerial: Aluminium.

Aluminium1Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 2026Aluminum alloy frame. The bezel is stainless steel according to the support FAQ.3Maker product pagemi.com/global/support/faq/details/KA-517264Read 15 October 2026Q2: middle frame entirely aluminium alloy, bezel stainless steel.

Case material (as published)

Aluminum1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Materials: the housing is aluminum. The store names the finishes Graphite, Platinum and Soft Gold Aluminum.

Aluminium alloy middle frame with PVD coating and stainless steel bezel3Maker product pagemi.com/global/support/faq/details/KA-517264Read 15 October 2026Q2 and the S3 comparison: aluminium alloy with PVD coating, stainless steel bezel.

BackiMaterial of the back of the smallest base-material case. Other materials or regional editions can differ. See source notes.

Not available

Not available

Case dimensionsiPhysical case height, width and thickness. The source note states exclusions such as the heart-rate sensor protrusion.

Height40.5Width40.5Thickness11.2mm(1.6 × 1.6 × 0.4 in)2Maker product pagestore.google.com/us/product/fitbit_sense_2_specsRead 23 October 2026Dimensions and weight: length 40.5 mm, width 40.5 mm, height 11.2 mm. The page states no sensor exclusion. The same page states weight 37.64 g without saying whether the band is included, so no weight is stored.

Height47.3Width47.3Thickness12mm(1.9 × 1.9 × 0.5 in)1Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 202647.3 x 47.3 x 12.0 mm. The maker excludes the strap and protrusions. The FAQ gives 14.13 mm thickness with the heart rate bump.3Maker product pagemi.com/global/support/faq/details/KA-517264Read 15 October 2026Q2: diameter 47.3 mm, thickness 12 mm excluding the deco and heart rate sensor.

Weight (case only)iWatch body without a strap. An unqualified published weight must not be assumed to exclude the strap.

Not available

44.5g(1.6 oz)1Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 202644.5 g approx., without the in-box strap.3Maker product pagemi.com/global/support/faq/details/KA-517264Read 15 October 2026Q2: 44.5 +/- 1 g, excluding the strap.

Weight with strapiWatch with the stated strap attached. Strap material and case size belong in the source note. Reviewer measurements belong in measured fields.

Not available

Not available

Durability

2 of 8 differ

Water resistanceiStatic water-pressure rating in atmospheres. It is not a safe swimming or diving depth. Diving limits are listed separately.

5ATM2Maker product pagestore.google.com/us/product/fitbit_sense_2_specsRead 23 October 2026Water resistance: water resistant to 50 m. The Google compare page states 5 ATM.9Maker product pagestore.google.com/gb/magazine/google_pixel_watch_compareRead 23 October 2026Maker comparison, Water and dust resistance row: Sense 2 5 ATM.

5ATM1Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 20265 ATM, described as 50 m static pressure. The maker says it is not suitable for hot showers, saunas or diving.3Maker product pagemi.com/global/support/faq/details/KA-517264Read 15 October 2026Q9: 5 ATM, equivalent to 50 m, for pool and shallow-water use and not for diving.

Water resistance standard

IEC 605291Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026IP Rating, printed page 78: Model FB521 has a water resistance rating of IPX8 under IEC 60529, up to a depth of 50 meters. IEC 60529 covers ingress, so no ISO pressure standard is inferred.

Not available

Dust and water rating

IP6X, IPX81Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026IP Rating: IPX8 under IEC 60529 up to 50 m, and IP6X dust-tight. Stored as the two published codes.

Not available

Dive rating

Not available

Not available

Max dive depthiMaker-rated depth for the stated diving use, not a conversion from the water-resistance pressure rating.

Not available

Not available

MIL-STD-810iMaker claim that the watch was tested against specified MIL-STD-810 methods. It is not a guarantee for every military-standard test.

Not available

Not available

MIL-STD-810 tests

Not available

Not available

Operating temperatureiPublished operating range. Source notes identify on-wrist limits and other operating conditions. Storage or charging limits are excluded.

Min-10Max45°C1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Environmental conditions, printed page 63: operating temperature 14 to 113 F (-10 to 45 C). Non-operating and charging ranges (0 to 35 C) are not stored.

Min-10Max45°C9Retailer pageteamplush.by/enRead 15 October 2026Same reseller copy of the manual: working temperature -10 to 45 C.

Display

6 of 14 differ

Display type

OLED2Maker product pagestore.google.com/us/product/fitbit_sense_2_specsRead 23 October 2026Display: AMOLED display.

OLED1Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 2026Spec row: 1.43-inch AMOLED display. No LTPO is stated.

Display type (as published)

AMOLED2Maker product pagestore.google.com/us/product/fitbit_sense_2_specsRead 23 October 2026Display: AMOLED display.

AMOLED1Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 2026Spec row: AMOLED display.

Screen sizeiPublished active display diagonal for a rectangular display, or diameter for a round display. Do not calculate it from pixels or display area.

1.58in(4 cm)12Spec databasegadgetsandwearables.com/technical-specs/fitbit-sense-2Read 23 October 2026Display size 1.58 inch. Notebookcheck and nextpit state the same. Fitbit publishes no diagonal.14Spec databasenextpit.de/smartwatches/google-fitbit-sense-2Read 23 October 2026Displaygröße: 1,58 Zoll.

1.43in(3.6 cm)1Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 20261.43-inch AMOLED display, 466 x 466 pixels.

Resolution

336 × 336px12Spec databasegadgetsandwearables.com/technical-specs/fitbit-sense-2Read 23 October 2026Display resolution 336 x 336 pixels. Notebookcheck states the same.

466 × 466px1Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 2026

Pixel densityiPublished pixel density. A rectangular diagonal formula must not be applied to a round display.

Not available

326ppi1Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 2026Published PPI 326.

Display area

Not available

Not available

Touchscreen

Yes1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Navigate Sense 2: color AMOLED touchscreen display and 1 button.

Yes1Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 2026

Max refresh rateiHighest published display refresh rate in active operation.

60Hz18Measurementnotebookcheck.net/Fitbit-Sense-2-Smartwatch-review-Automatic-activity-recording.717608.0.htmlRead 23 October 2026Notebookcheck spec box lists 60 Hz. Fitbit publishes no refresh rate. Treated as a stated spec, not a measurement.

60Hz1Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 202660 Hz refresh rate. The maker notes it may vary across interfaces.

Min refresh rateiLowest published display refresh rate, usually in always-on mode. It is not the active-use minimum unless stated.

Not available

Not available

Peak brightnessiMaker peak-brightness claim. It may apply to a small area or bright ambient light. Full-screen limits and battery/temperature conditions belong in source notes.

1,000nits12Spec databasegadgetsandwearables.com/technical-specs/fitbit-sense-2Read 23 October 2026Display brightness: Up to 1,000 nits. Fitbit publishes no nit figure in the documents read, so this is a spec database claim. Window size and ambient conditions are not stated.

2,200nits1Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 2026Peak 2200 nits is when only part of the screen lights up. HBM 1500 nits is the full-screen maximum. No reviewer measurement is substituted.

Minimum brightness

Not available

Not available

Always-on display

Yes1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Adjust always-on display section. The setting reduces battery life.3Maker product pagestore.google.com/us/product/fitbit_sense_2Read 23 October 2026Always-on display mode: keeps your display on at all times (may require more frequent charging).

Yes2Maker product pagemi.com/global/product/xiaomi-watch-s4Read 15 October 2026Support FAQ has the AOD controls. The overview page announces colour always-on displays.3Maker product pagemi.com/global/support/faq/details/KA-517264Read 15 October 2026Q26: Always-on display supported, with Smart or Scheduled modes.

Display cover

Gorilla Glass2Maker product pagestore.google.com/us/product/fitbit_sense_2_specsRead 23 October 2026Display: Corning Gorilla Glass 3.

Other glass3Maker product pagemi.com/global/support/faq/details/KA-517264Read 15 October 2026Q2: Panda Glass cover. It is not a named Gorilla Glass or sapphire.

Display cover (as published)

Corning Gorilla Glass 32Maker product pagestore.google.com/us/product/fitbit_sense_2_specsRead 23 October 2026Display: Corning Gorilla Glass 3.

Panda Glass3Maker product pagemi.com/global/support/faq/details/KA-517264Read 15 October 2026Q2: Panda Glass.

Platform

10 of 15 differ

Platform

Proprietary2Maker product pagestore.google.com/us/product/fitbit_sense_2_specsRead 23 October 2026No OS name is printed on the spec page. The Fitbit blog says the watch is powered by the new Fitbit OS, a proprietary platform with its own Gallery.

Proprietary1Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 2026Operating system: Xiaomi HyperOS 2, Xiaomi's own software. No Wear OS or other third-party watch platform is named.

OS at launch

Fitbit OS4Press releaseblog.google/products-and-platforms/devices/fitbit/versa-4-sense-2Read 23 October 2026Powered by the new Fitbit OS. No version number is published.

Xiaomi HyperOS 21Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 2026

Software

Not available

Not available

Latest OS

Fitbit OS, firmware 220.317Maker product pagesupport.google.com/googlehealth/answer/14236725Read 23 October 2026Fitbit firmware release notes: Sense 2 latest listed version 220.31 (bug fixes and improvements) on the access date. No Fitbit OS major version number is published.

Not available

Works with

iOS, Android2Maker product pagestore.google.com/us/product/fitbit_sense_2_specsRead 23 October 2026Requirements: Apple iOS 16.4 or higher, Android OS 11.0 or higher, current on the access date.

Android, iOS1Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 2026Supports Android 8.0 and above, or iOS 14.0 and above.

Phone requirement

Google Health app on a compatible device running Apple iOS 16.4 or higher or Android OS 11.0 or higher2Maker product pagestore.google.com/us/product/fitbit_sense_2_specsRead 23 October 2026Requirements: the Google Health app on a device running Apple iOS 16.4 or higher or Android OS 11.0 or higher. This is the current requirement. The 2022 launch requirement may have been lower.

Android 8.0 or later, or iOS 14.0 or later, with the Mi Fitness app1Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 2026The Mi Fitness app is required for pairing according to the support FAQ.

App store

No1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026The Fitbit Gallery offers Fitbit apps and clock faces. Tom's Guide states third-party apps cannot be downloaded.17Reviewtomsguide.com/news/fitbit-sense-2Read 23 October 2026Review: you don't get access to third-party apps. You can download custom watch faces but not third-party apps. The Sense 2 and Versa 4 cannot.

Not available

Voice assistants

Amazon Alexa1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Voice Assistant: Amazon Alexa Built-in. Needs the phone app running in the background. Not available in all countries.3Maker product pagestore.google.com/us/product/fitbit_sense_2Read 23 October 2026Smarts and more: Alexa Built-in.

Not available

Chipset

Ambiq Apollo4 Plus12Spec databasegadgetsandwearables.com/technical-specs/fitbit-sense-2Read 23 October 2026Platform: Ambiq Apollo4 Plus, ARM Cortex-M4 at 96-192 MHz. Fitbit publishes no chip and Notebookcheck says it does not disclose the SiP. Ambiq's own presentation says Apollo4 powers the Sense product line, which supports the chip family but not the Plus suffix.16Press articleambiq.com/wp-content/uploads/2022/12/Key-to-the-Future-of-Electronics.pdfRead 23 October 2026Ambiq presentation: Apollo4 powers Inspire, Versa and Sense product lines of Fitbit, and Versa 4, Sense 2 and Inspire 3 were launched in August 2022.

Not available

Process

Not available

Not available

CPU cores

112Spec databasegadgetsandwearables.com/technical-specs/fitbit-sense-2Read 23 October 2026Same Platform entry: one ARM Cortex-M4 core.

Not available

CPU configuration

AFitbit Sense 2

Count	Core	Max clock (GHz)
1	Arm Cortex-M4	0.192

Source12Spec databasegadgetsandwearables.com/technical-specs/fitbit-sense-2Read 23 October 2026Same Platform entry: ARM Cortex-M4 at 96-192 MHz. 192 MHz is stored as the maximum.

BXiaomi Watch S4

Not available

Max CPU clock

0.192GHz=CalculatedFrom CPU configuration

Not available

GPU

Not available

Not available

Low-power coprocessor

Not available

Not available

Memory

2 of 2 differ

RAMiKeep published GB values as stated. Convert a source explicitly labelled MB using 1000 MB per GB and preserve its original figure and unit in the note. Do not assume MB means MiB. Convert explicit MiB or GiB to decimal GB through their byte definitions, recording the conversion in the note. This normalization does not establish an exact physical byte count.

2.75 MB12Spec databasegadgetsandwearables.com/technical-specs/fitbit-sense-2Read 23 October 2026Same entry: 2.75 MB on-chip SRAM, stored as 0.00275 GB with 1000 MB per GB. No maker figure exists.

Not available

StorageiTotal built-in storage the maker states, in decimal GB. Space available to the user is lower and goes in the source note. A figure the maker gives only as available space is not stored.

4GB18Measurementnotebookcheck.net/Fitbit-Sense-2-Smartwatch-review-Automatic-activity-recording.717608.0.htmlRead 23 October 2026Performance and runtime: the manufacturer has installed 4 GB of internal storage, usable for apps and watch faces. Fitbit publishes no storage figure. Routes and music cannot be stored.

Not available

Health sensors

7 of 8 differ

Heart rate sensor

Multi-path optical heart rate sensor1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Sensors and Components: multi-path optical heart rate tracker. The Google Store spells it Multi-path optical heart rate sensor.2Maker product pagestore.google.com/us/product/fitbit_sense_2_specsRead 23 October 2026Sensors and components: multi-path optical heart rate sensor.

Heart rate sensor (with blood oxygen sensor)1Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 2026Sensors row: heart rate sensor (with blood oxygen sensor). No sensor generation is named.

ECG capabilityiElectrical heart sensing hardware with an ECG capability. The ECG app can require an eligible country, age and paired phone.

Yes1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Sensors and Components: multipurpose electrical sensors compatible with the ECG app and EDA Scan app. The ECG app is not available in all countries.2Maker product pagestore.google.com/us/product/fitbit_sense_2_specsRead 23 October 2026Sensors: multipurpose electrical sensors compatible with ECG app and EDA app. ECG not available in all countries.

Not available

Blood oxygen sensingiBlood-oxygen sensing capability. App availability and medical status vary by market.

Yes1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Sensors and Components: red and infrared sensors for oxygen saturation (SpO2) monitoring.

Yes1Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 2026

Skin temperature sensingiA sensor or supported function that measures skin temperature. It is not a core-body thermometer.

Yes1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Sensors and Components: on-wrist skin temperature sensor. Track your skin temperature changes: nightly variation from a personal baseline. Not available in all markets.

Not available

Blood pressure featureiPublished blood-pressure feature category. Hypertension notifications are not numerical blood-pressure readings.

None12Spec databasegadgetsandwearables.com/technical-specs/fitbit-sense-2Read 23 October 2026Blood pressure: No. The maker sensor list and feature pages have no blood-pressure feature.

Not available

Body composition sensor

No1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026The complete sensor list in Sensors and Components has no bioelectrical impedance sensor.12Spec databasegadgetsandwearables.com/technical-specs/fitbit-sense-2Read 23 October 2026Body composition: No.

Not available

Skin conductance (EDA)

Yes1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Sensors and Components: electrical sensor to measure skin conductance (cEDA) for stress detection. Manage stress: continuous EDA identifies body responses.4Press releaseblog.google/products-and-platforms/devices/fitbit/versa-4-sense-2Read 23 October 2026Sense 2 has a new Body Response sensor for continuous electrodermal activity (cEDA).

Not available

Medical clearancesiNamed regulatory clearances and their jurisdiction. General water resistance or an ECG sensor does not establish medical clearance.

ECG app: FDA clearance, ECG app: EU clearance, Irregular Heart Rhythm Notifications: FDA clearance, Irregular Heart Rhythm Notifications: EU clearance3Maker product pagestore.google.com/us/product/fitbit_sense_2Read 23 October 2026Heart section: the ECG app assesses heart rhythm for atrial fibrillation. Clearance wording is in the Fitbit blog.5Press releaseblog.google/products-and-platforms/devices/fitbit/fitbit-sense-2-versa-4Read 23 October 2026Footnote and text: the ECG app on Sense 2 and the Irregular Heart Rhythm Notifications on both watches have FDA and EU clearance. Only in select countries, not for people under 22 or with known atrial fibrillation.

Not available

Motion and environment sensors

1 of 9 differ

Accelerometer

Yes1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Sensors and Components: 3-axis accelerometer.2Maker product pagestore.google.com/us/product/fitbit_sense_2_specsRead 23 October 2026Sensors and components: 3-axis accelerometer.

Yes1Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 2026

Accelerometer range

Not available

Not available

Gyroscope

Yes1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Sensors and Components: gyroscope.

Yes1Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 2026

Barometric altimeter

Yes1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Sensors and Components: altimeter, which tracks altitude changes.

Yes1Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 2026

Compass

No1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026The complete sensor list in Sensors and Components has no compass or magnetometer. Gadgets & Wearables also lists Compass: No.12Spec databasegadgetsandwearables.com/technical-specs/fitbit-sense-2Read 23 October 2026Compass: No. Geomagnetic: No.

Yes1Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 2026Sensors row lists an electronic compass.

Ambient light sensor

Yes1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Sensors and Components: ambient light sensor.

Yes1Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 20263Maker product pagemi.com/global/support/faq/details/KA-517264Read 15 October 2026Brightness Auto adjusts to ambient light.

Depth gauge

Not available

Not available

Depth gauge rangeiPublished measurement range of the depth gauge, distinct from maximum diving depth and water-pressure resistance.

Not available

Not available

Water temperature sensor

Not available

Not available

Health and fitness

2 of 5 differ

Health featuresiSupported health functions with country, phone and subscription restrictions in the source notes. Upcoming functions are not counted as available.

Continuous heart rate, Heart rate alerts, Irregular rhythm notifications, ECG app, Blood oxygen app, Heart rate variability, Sleep tracking, Sleep stages, Stress tracking, Readiness score, Cycle tracking1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Today and sleep sections: sleep stages (REM, light, deep) and sleep score, stress management score, readiness score (Premium), menstrual health tile, high and low heart rate notifications after 10 inactive minutes, heart-rate variability under Advanced health metrics, oxygen saturation. Daily readiness score needs Fitbit Premium. Irregular rhythm notifications and the ECG app come from the Fitbit blog.3Maker product pagestore.google.com/us/product/fitbit_sense_2Read 23 October 2026Heart rate tracking, high and low heart rate notifications, irregular heart rhythm notifications, ECG app, HRV, breathing rate, SpO2, sleep tracking and sleep stages, Stress Management Score, Daily Readiness Score, menstrual health tracking. The Daily Readiness Score is a Premium feature in the manual.

Continuous heart rate, Blood oxygen app, Sleep tracking, Sleep stages, Stress tracking, Cycle tracking2Maker product pagemi.com/global/product/xiaomi-watch-s4Read 15 October 2026Overview: heart rate, stress, blood oxygen and sleep monitoring, all-day options that need to be switched on. These are not medical features.3Maker product pagemi.com/global/support/faq/details/KA-517264Read 15 October 2026Health pages: all-day heart rate, blood oxygen and stress, sleep stages (deep, light, REM, awake) and the Cycles app.

Fitness featuresiSupported workout functions. A sport-profile name alone does not prove advanced metrics such as running power or running dynamics. Trackback follows the recorded route back to the start. A compass arrow that points straight to the start does not count.

Automatic workout detection, VO2 max, Pool swim, Interval workouts, Turn-by-turn navigation1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Exercise settings list Pool Length, Interval, Auto Start and Auto-Stop. Track your exercise automatically (SmartTrack, 15 minute minimum). Google Maps gives turn-by-turn directions and needs the paired phone nearby with the app running. View your cardio fitness score (stored as vo2_max, see the Google Health VO2 max help page).3Maker product pagestore.google.com/us/product/fitbit_sense_2Read 23 October 2026Fitness features: Cardio Fitness Score estimated from VO2 max, SmartTrack Automatic Exercise Recognition (in app only), Google Maps turn-by-turn directions.11Maker product pagesupport.google.com/googlehealth/answer/14237924Read 23 October 2026Learn about your VO2 max: VO2 max, formerly the cardio fitness score, is estimated during outdoor runs with GPS. The Sense 2 manual names the cardio fitness score.

Automatic workout detection, VO2 max, Training load, Running dynamics, Pool swim, Open water swim2Maker product pagemi.com/global/product/xiaomi-watch-s4Read 15 October 2026Overview: running form recognition (vertical ratio, vertical amplitude, ground contact time) and 150+ sports modes.3Maker product pagemi.com/global/support/faq/details/KA-517264Read 15 October 2026Workout Q1: auto detect for walking, running, cycling, rower, elliptical and jump rope. Q2 workout data: vertical stride ratio, vertical amplitude and ground contact time in running. 17 modes give pro data including pool and open water swimming. The Training State app manages training load.11Retailer pageeuronics.ee/en/phones/watches/smart-watches/bhr9195gl/xiaomi-watch-s4-black-smart-watchRead 15 October 2026Retailer spec tab lists maximal oxygen uptake (VO2 max) measurements as Yes.

Sport profilesiPublished count of distinct sport/activity profiles. A claim such as 180+ is not an exact integer count.

Not available

Not available

Dive modesiActual supported dive modes. Water resistance or a depth app alone does not establish decompression-capable scuba support.

Not available

Not available

External sensorsiTypes of external workout sensors the watch can pair with. GPS reception, phone data and built-in sensors do not qualify.

Not available

Not available

Safety

4 of 6 differ

Fall detectioniAutomatic fall detection. Incident detection restricted to recorded workouts is not counted as general fall detection.

No9Maker product pagestore.google.com/gb/magazine/google_pixel_watch_compareRead 23 October 2026Safety and emergency rows (Safety Check, Emergency Sharing, Medical information, Fall Detection, Emergency SOS, Emergency international calling, Car Crash Detection, Earthquake Alerts): the Sense 2 column is empty for all of them. No fall detection.

Not available

Car crash detection

No9Maker product pagestore.google.com/gb/magazine/google_pixel_watch_compareRead 23 October 2026Same Safety rows: Car Crash Detection is empty in the Sense 2 column.

Not available

Emergency SOSiA manual emergency alert to emergency services or preset contacts. Source notes identify the recipient, paired-phone requirement and country limits. Satellite is listed separately.

No9Maker product pagestore.google.com/gb/magazine/google_pixel_watch_compareRead 23 October 2026Same Safety rows: Emergency SOS is empty in the Sense 2 column.

Not available

Emergency sireniPublished or measured siren sound level in decibels. Audible distance alone does not establish this value. Measurement distance belongs in source notes.

Not available

Not available

Live location sharingiShares live location during supported use. A paired phone or data subscription may be required.

Not available

Not available

Dedicated LED flashlightiA dedicated hardware LED flashlight. Lighting the display white is not counted.

No9Maker product pagestore.google.com/gb/magazine/google_pixel_watch_compareRead 23 October 2026No flashlight appears in the Sense 2 sensor and component list. Gadgets & Wearables states Flashlight: No.12Spec databasegadgetsandwearables.com/technical-specs/fitbit-sense-2Read 23 October 2026Flashlight: No.

Not available

Positioning

3 of 3 differ

PositioningiPublished satellite systems and signal bands. Do not infer bands from dual-frequency support alone.

GPS, GLONASS1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Sensors and Components: built-in GPS receiver + GLONASS. Dynamic GPS can use the phone's GPS instead to save battery. No band or dual-frequency claim.4Press releaseblog.google/products-and-platforms/devices/fitbit/versa-4-sense-2Read 23 October 2026Built-in GPS is named for Sense 2.

GPS (L1 + L5), Galileo (E1 + E5a), GLONASS (G1), BeiDou (B1I + B1C + B2a), QZSS (L1 + L5)1Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 2026Satellite systems: GPS, Galileo, Glonass, BeiDou and QZSS. The overview page says L1+L5 dual-frequency GNSS. The per-constellation bands come from the reseller copy of the manual regulatory table.7Spec databasegsmarena.com/xiaomi_watch_s4-13476.phpRead 15 October 2026Positioning: GPS (L1+L5), GLONASS, GALILEO, BDS, QZSS.9Retailer pageteamplush.by/enRead 15 October 2026Reseller page reproducing the M2425W1 manual regulatory table: GPS L1 / Galileo E1 / GLONASS G1 / BDS B1I, B1C / QZSS L1 at 1559-1610 MHz, and GPS L5 / Galileo E5a / BDS B2A / QZSS L5 at 1164-1215 MHz. This agrees with the maker's L1+L5 claim and GSMArena. Xiaomi's own manual PDF was not found, so the reseller copy is the source.

Dual-band GNSSiMaker-stated dual-frequency satellite reception. Supported constellations and signal bands are listed separately.

Not available

Yes2Maker product pagemi.com/global/product/xiaomi-watch-s4Read 15 October 2026Overview: L1+L5 dual-frequency GNSS of five satellite positioning systems from an independent chip.

Offline mapsiMap data stored on the watch and usable without live phone data. GPX routes or breadcrumb tracks alone are not offline maps.

No12Spec databasegadgetsandwearables.com/technical-specs/fitbit-sense-2Read 23 October 2026Offline maps: No. The manual requires the phone and background app for Google Maps.

Not available

Connectivity

4 of 15 differ

BluetoothiPublished Bluetooth support for this model. The version is recorded separately. Unknown version does not mean the radio is absent.

Yes1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Wireless technology: Bluetooth 5.0 radio transceiver and NFC chip.

Yes1Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 2026

Bluetooth version

5.01Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Wireless technology, printed page 62: Bluetooth 5.0 radio transceiver and NFC chip.14Spec databasenextpit.de/smartwatches/google-fitbit-sense-2Read 23 October 2026Bluetooth: 5.

5.31Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 2026Wireless connectivity: Bluetooth 5.3.7Spec databasegsmarena.com/xiaomi_watch_s4-13476.phpRead 15 October 2026Bluetooth 5.3, A2DP, LE.9Retailer pageteamplush.by/enRead 15 October 2026The copied table lists Bluetooth 5.3 at 2400-2483.5 MHz.

Wi-FiiPublished Wi-Fi support for this model. The standard and bands are recorded separately. Unknown standard does not mean Wi-Fi is absent.

No1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Sensors and Components: WiFi (deactivated, cannot be turned on). Stored as false because the user cannot use it. No Wi-Fi standard is stored.

No7Spec databasegsmarena.com/xiaomi_watch_s4-13476.phpRead 15 October 2026WLAN: No.9Retailer pageteamplush.by/enRead 15 October 2026The copied radio table lists only GNSS, Bluetooth and NFC, with no Wi-Fi radio.

Wi-Fi standard

Not available

Not available

Wi-Fi bands

Not available

Not available

CellulariTrue when a cellular edition is sold. A variant row states whether that individual model has cellular hardware.

No1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026No cellular radio is listed in Wireless technology (Bluetooth and NFC only).

No7Spec databasegsmarena.com/xiaomi_watch_s4-13476.phpRead 15 October 2026Versions: eSIM and NFC (China), Bluetooth and NFC (China), Bluetooth only (International). The global page and the EU declaration list no cellular radio, so the global model has no cellular.

Network

Not available

Not available

4G bandsiPublished LTE bands for the stated regional cellular model. Do not transfer bands to another region or Wi-Fi-only model.

Not available

Not available

5G bandsiPublished 5G NR bands for the stated regional cellular model. RedCap support does not establish conventional full-bandwidth phone 5G.

Not available

Not available

NFCiSome regions sell an NFC edition, so it is per variant.

Yes1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Wireless technology: NFC chip. Contactless Payments section describes the built-in NFC chip.

Yes1Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 2026NFC: Supported. The maker says availability may vary by region.9Retailer pageteamplush.by/enRead 15 October 2026The copied regulatory table lists an NFC operating frequency of 13.56 MHz.

Contactless payments

Yes1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Contactless Payments: set up Google Wallet in the Fitbit app and pay at contactless terminals.3Maker product pagestore.google.com/us/product/fitbit_sense_2Read 23 October 2026Smarts and more: Google Wallet, make purchases from your wrist everywhere Google Pay is accepted.

Yes2Maker product pagemi.com/global/product/xiaomi-watch-s4Read 15 October 2026NFC payment supports Mastercard and Visa terminals. Availability varies by region and issuing bank.

Payment services

Google Wallet1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Contactless Payments: Google Wallet. The text also names Fitbit Pay for the older service name.

Xiaomi Pay3Maker product pagemi.com/global/support/faq/details/KA-517264Read 15 October 2026NFC related: bank cards are added through Mi Fitness, Device, Apps, Xiaomi Pay.

Ultra-wideband

No1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Wireless technology lists only a Bluetooth radio and an NFC chip. No UWB radio.

Not available

Satellite

None9Maker product pagestore.google.com/gb/magazine/google_pixel_watch_compareRead 23 October 2026No satellite feature in any Safety row. Published radios are Bluetooth and NFC. GPS reception is separate.

Not available

ANT+

Not available

Not available

Audio

2 of 4 differ

Speaker

Yes1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Sensors and Components lists Speaker and Microphone. The Google Store rates the speaker at 75 dB SPL at 10 cm. That is not an emergency siren.

Yes1Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 2026

Microphones

Not available

21Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 2026Spec row: 2 mics.

Calls on the watchiVoice-call capability of the marketed model, including sold cellular editions. Variant radio capability and paired-phone requirements still apply.

Phone only1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Answer or reject phone calls and Take on-wrist phone calls: calls go through the paired iPhone or Android phone, which must be nearby with the Fitbit app running. No cellular model exists.

Phone only1Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 2026Bluetooth calling: Supported while the watch stays connected to the phone's Bluetooth. Voice calls from third-party apps are not supported.

Music on the watchiPlays audio stored on the watch. Remote control of phone playback or streaming alone does not qualify.

No12Spec databasegadgetsandwearables.com/technical-specs/fitbit-sense-2Read 23 October 2026On-board music storage: No. Smartphone music control only.

Yes3Maker product pagemi.com/global/support/faq/details/KA-517264Read 15 October 2026Q28: local music playback on the watch. An Android phone downloads the music. An iPhone cannot download songs, but songs already on the watch play.

Controls

3 of 5 differ

ButtonsiPhysical controls used to operate the watch, excluding the rotating crown and strap-release buttons. A clickable rotating crown is counted only in Crown.

11Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Navigate Sense 2: color AMOLED touchscreen display and 1 button.

13Maker product pagemi.com/global/support/faq/details/KA-517264Read 15 October 2026Q2: the 2 o'clock position has the function button and rotating crown. The 4 o'clock position has the power button. The crown is counted only in Crown.

Named operating buttonsiNames of operating buttons, excluding the crown and strap-release controls.

Button1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Navigate Sense 2: the single button opens the apps menu, returns to the clock face and has long-press and double-press shortcuts.

Power button (4 o'clock)3Maker product pagemi.com/global/support/faq/details/KA-517264Read 15 October 2026Q2: power button at 4 o'clock.

CrowniA crown that rotates to control the interface. A round push button that does not rotate is not a crown.

None1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Navigate Sense 2 describes only the touchscreen and 1 button. No crown.

Rotating2Maker product pagemi.com/global/product/xiaomi-watch-s4Read 15 October 2026The overview describes a classic rotating crown.3Maker product pagemi.com/global/support/faq/details/KA-517264Read 15 October 2026Q2: stainless steel rotating crown that also works as a function button.

Rotating bezeliPhysical rotation or touch gestures around the display edge. A fixed decorative bezel is None.

None1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Navigate Sense 2 describes only the touchscreen and 1 button. No bezel control.

None3Maker product pagemi.com/global/support/faq/details/KA-517264Read 15 October 2026Q11: the bezel is a removable decorative part that twists on for installation. The maker describes no bezel input.

Gestures

Turn your wrist, Briefly cover the watch face with your opposite hand, Triple-tap the screen1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Screen wake setting: Button & motion turns the screen on when you turn your wrist. Turn off the screen: briefly cover the watch face with your opposite hand, except with always-on display. Screen Zoom: Magnify works on a triple-tap.

Raise to wake, Double-tap to wake, Wrist flip, Wrist shake, Finger snap, Fist clench2Maker product pagemi.com/global/product/xiaomi-watch-s4Read 15 October 2026Quick gestures and a classic rotating crown are listed. The support FAQ names the gestures.3Maker product pagemi.com/global/support/faq/details/KA-517264Read 15 October 2026Q24 lists wrist flip, wrist shake, finger snap and fist. Fist works only with HyperOS 2 phones. Raise to wake and double-tap to wake are in the display settings.

Battery and charging

8 of 13 differ

Battery capacityiPublished battery capacity for the stated case size. Rated and typical capacity are distinguished in source notes.

162mAh12Spec databasegadgetsandwearables.com/technical-specs/fitbit-sense-2Read 23 October 2026Battery: rechargeable lithium-polymer battery, 162 mAh.13Retailer pageifixit.com/products/fitbit-sense-2-batteryRead 23 October 2026iFixit replacement battery listing for Sense 2: 0.62 Wh, 3.87 V, 162 mAh. 162 mAh x 3.87 V = 0.627 Wh, which agrees. It is a parts listing, not a teardown. Gadgets & Wearables, Notebookcheck and nextpit also state 162 mAh. Two Argos listings print 260 mAh, which is not used.14Spec databasenextpit.de/smartwatches/google-fitbit-sense-2Read 23 October 2026Batteriekapazität (Netto): 162 mAh.

486mAh1Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 2026Capacity 486 mAh. Rated or typical is not stated.

Claimed battery lifeiMaker endurance claims with distinct operating modes and case sizes. With solar describes augmentation of that estimate, not hardware capability. Use false for ordinary claims without solar augmentation, true for explicitly solar-aided claims, and omit it when solar qualification is unclear. Source notes state AOD, GNSS, music and solar conditions. Do not create a normal-use row from an AOD-only claim. Low power denotes the maker battery-saver mode. Keep its typical, light-use and always-on claims separate from standard-mode claims. GPS power saving identifies an intermediate reduced-accuracy GNSS saving preset. Source notes retain the maker's preset name and published conditions. Max battery GPS is the distinct maximum-saving claim. When the maker has only one GPS saving preset, it is GPS power saving.

AFitbit Sense 2

Mode	With solar	Hours (h)
Smartwatch	No	144
Always-on	No	72
GPS	No	5

Source2Maker product pagestore.google.com/us/product/fitbit_sense_2_specsRead 23 October 2026Battery and power: battery life of 6+ days, stored as 144 h as a minimum figure. Up to 5 hours with continuous GPS, stored as the gps row. The always-on display, SpO2 and cEDA sensor need more frequent charging. The Google Health support article states up to 12 hours with continuous GPS for Sense 2, a conflict. The model spec page is used because the Oct 2022 Fitbit.com page printed the same 5 hours.6Maker product pagesupport.google.com/googlehealth/answer/14226518Read 23 October 2026Estimated battery life table: Fitbit Sense 2 6+ days. Footnote: with always-on display, Sense 2 has a battery life of up to 3 days (stored as 72 h always_on). The same footnote says Sense 2 has up to 12 hours with continuous GPS, which conflicts with the 5 hours on the model spec page. The 12 hour figure is not stored.10Maker product pageweb.archive.org/web/20221022073607/https://www.fitbit.com/global/us/products/smartwatches/sense2Read 23 October 2026Archived Fitbit.com Sense 2 page, Oct 22, 2022: battery life of 6+ days and up to 5 hours with continuous GPS. Same wording as the current Google Store.

BXiaomi Watch S4

Mode	With solar	Hours (h)
Smartwatch	No	360
Always-on	No	120

Source2Maker product pagemi.com/global/product/xiaomi-watch-s4Read 15 October 2026Up to 15 days typical usage, tested by Xiaomi Internal Labs with factory defaults, AOD off, 100 messages a day, 200 wrist raises a day, 90 minutes of GNSS sports a week and 10-minute heart rate checks. The FAQ gives 14.5 days with an iPhone and 5 days with the Smart AOD option on. Days are converted exactly to hours.3Maker product pagemi.com/global/support/faq/details/KA-517264Read 15 October 2026Charging and Battery Q1: typical 15 days (14.5 with an iPhone) and AOD 5 days, with the stated test conditions.

Smartwatch mode (claimed)iMaker normal-use smartwatch claim without solar. A watch with only an explicit AOD-mode claim has no value here. Workloads differ and source notes must be read.

144h=CalculatedFrom Claimed battery life

360h=CalculatedFrom Claimed battery life

AOD battery life (up to)iMaker claimed smartwatch endurance with the always-on display enabled and without solar, for the base case. Source notes preserve workload and case conditions. This is a claim, not a measured test or an AOD-off estimate.

72h=CalculatedFrom Claimed battery life

120h=CalculatedFrom Claimed battery life

GPS mode (claimed)iMaker regular GPS/GNSS activity claim without solar, for the base case. AOD, multi-band, music and power-saving conditions have separate rows when published.

5h=CalculatedFrom Claimed battery life

Not available

Solar chargingiPublished solar charging hardware capability. An ordinary battery estimate without solar augmentation does not prove that the watch lacks solar charging hardware.

Not available

Not available

Charging methodiThe connection at the watch, not the cable end at the USB adapter. A proprietary inductive puck is not Qi unless interoperability is explicitly established.

Magnetic pins1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Charge your watch: hold the cable end near the port on the back until it attaches magnetically. The pins on the cable align with the port on the back.

Magnetic pins1Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 2026Charging port: 2-pin magnetic charging dock.

Charging guidanceiPublished charging requirements, nominal estimates and compatibility guidance. Keep adapter ratings separate from power accepted by the watch.

Not available

2-pin magnetic charging dock with a USB-A cable. The FAQ asks for a USB-A charger with 5 V output and at least 0.5 A.1Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 2026The support FAQ gives the supply requirement.3Maker product pagemi.com/global/support/faq/details/KA-517264Read 15 October 2026Charging Q2: USB-A charger with 5 V and at least 0.5 A output.

Max charging power (watch)iPublished maximum charging power at the watch. Adapter rating or charger input power does not prove the power accepted by the watch.

Not available

Not available

Fast chargingiAn explicit fast-charging capability claim. A short charging time or high adapter wattage alone does not qualify.

Yes5Press releaseblog.google/products-and-platforms/devices/fitbit/fitbit-sense-2-versa-4Read 23 October 2026Fast charging gets a full day's worth of battery in just 12 minutes.

Yes2Maker product pagemi.com/global/product/xiaomi-watch-s4Read 15 October 2026Overview headline: 5 minutes of fast charging delivers 2 days of usage.

Quick charge claimiMaker claim for usage from a short charge. Source notes identify the usage workload, such as normal use or sleep tracking.

Charge time12 minUse time24 h1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Charge your watch: charge Sense 2 for 12 minutes for 24 hours of battery life. The usage workload is not named.

Charge time5 minUse time48 h2Maker product pagemi.com/global/product/xiaomi-watch-s4Read 15 October 20265 minutes of charging for 2 days of usage. The FAQ says this follows the typical battery model, which is the typical-use workload.3Maker product pagemi.com/global/support/faq/details/KA-517264Read 15 October 2026Charging Q1: 5 minutes of charging provides a 2-day boost under the typical battery model.

Charge 0 to 80% (claimed)iMaker claim for charging an empty battery to 80%. Charger and approximate qualifiers belong in source notes.

Not available

Not available

Full charge time (claimed)iMaker advertised nominal full-charge duration. Approximate or theoretical maker estimates are allowed, with their conditions in source notes. Partial-charge intervals do not qualify. Measured 0 to 100% tests have a separate field.

120min1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Charge your watch: charging fully takes about 1-2 hours. The Google Store spec page states two hours and is stored.2Maker product pagestore.google.com/us/product/fitbit_sense_2_specsRead 23 October 2026Battery and power: the Oct 2022 Fitbit.com spec text states charge time (0-100%): two hours.

60min3Maker product pagemi.com/global/support/faq/details/KA-517264Read 15 October 2026Charging Q1 and Q2: about 60 minutes to fully charge.

Measured

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Peak brightness (measured)iReviewer measurement. Source notes state screen area, mode and ambient light. A small-area peak claim cannot be replaced with a full-screen measurement.

Not available

Not available

Battery life (measured)iReviewer-observed mixed-use endurance. Source notes state case size, AOD, workout use and whether it was a complete discharge. Extrapolation from partial discharge is excluded.

144h18Measurementnotebookcheck.net/Fitbit-Sense-2-Smartwatch-review-Automatic-activity-recording.717608.0.htmlRead 23 October 2026Battery life: with all measurements active, worn around the clock, automatic training detection on, no extensive workouts and the always-on display off, the Sense 2 lasts exactly six days (144 h). Firmware and brightness are not stated. The always-on display test (just under four days) has no exact figure and is not stored.

Not available

Battery tests (measured)iReviewer-observed endurance, with case size and test settings in source notes. Partial-discharge projections are not stored as measured endurance.

AFitbit Sense 2

Test	Hours (h)
Mixed use, always-on display off	144

Source18Measurementnotebookcheck.net/Fitbit-Sense-2-Smartwatch-review-Automatic-activity-recording.717608.0.htmlRead 23 October 2026Same test: always-on display off, all measurements active, automatic training detection, no extensive workouts. 6 days converted to 144 h. With the always-on display on it lasted just under four days, which is not stored as a number.

BXiaomi Watch S4

Test	Hours (h)
Mixed use, always-on	48

Source8Reviewgsmarena.com/xiaomi_watch_s4_review-news-67715.phpRead 15 October 2026Reviewer used AOD, notifications, a one-hour daily workout and sleep tracking. The most was three days when the watch nearly died, and two days was a consistent result. Stored as about 48 hours. Firmware and display brightness are not stated.

Full charge time (measured)iReviewer measurement from empty to full, not 0-80% or a charge from 5%. Source notes name the charger and case size.

95min18Measurementnotebookcheck.net/Fitbit-Sense-2-Smartwatch-review-Automatic-activity-recording.717608.0.htmlRead 23 October 2026Battery life: 0 to 99 percent after 85 minutes on a 24-watt power supply and another 10 minutes for the last percent. Stored as 95 minutes for 0 to 100 percent. 0 to 80 percent took one hour. Test unit with the supplied charging cable and a 24 W adapter. The maker claims two hours.

Not available

Strap

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Lug widthiDistance between standard strap attachment lugs, not the decorative width of a proprietary strap. Unknown for custom connectors unless the maker publishes lug width.

24mm3Maker product pagestore.google.com/us/product/fitbit_sense_2Read 23 October 2026The store shows an accessory shop headed Shop 24mm attach accessories. Fitbit publishes no lug width in a spec table, and the connector is proprietary, so this is the maker's attach size only.18Measurementnotebookcheck.net/Fitbit-Sense-2-Smartwatch-review-Automatic-activity-recording.717608.0.htmlRead 23 October 2026Case and features: the strap is 24 millimeters wide and can be changed without tools. It is not a standard clasp, so 24 mm is the strap width, not a lug width for standard straps.

22mm3Maker product pagemi.com/global/support/faq/details/KA-517264Read 15 October 2026Q7: strap width 22 mm.

Quick-release strapiThe supplied strap can be detached through its quick-release mechanism. Compatibility with quick-release replacement straps alone does not qualify.

Yes1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Change the band: slide the flat latch button toward the band, pull the band away. Attach by pressing until it clicks. No tools.

Yes3Maker product pagemi.com/global/support/faq/details/KA-517264Read 15 October 2026Q6: the watch supports quick-release straps released through the spring bar.

Strap systemiPublished attachment system and compatible case sizes. Proprietary connectors are distinguished from standard spring bars.

Proprietary latch connector. Fitbit Sense, Versa 3 and Versa 4 bands are compatible.1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Change the band: Fitbit Sense, Fitbit Versa 3, and Fitbit Versa 4 bands are compatible with Sense 2. Band latches on the back. No lug width is stated in the manual.

22 mm quick-release straps with spring bars3Maker product pagemi.com/global/support/faq/details/KA-517264Read 15 October 2026Q6 and Q7: quick-release spring-bar straps, any 22 mm strap.

Strap materialiMaterial of the supplied strap for the stated package. Do not substitute material from another band sold separately.

Other1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Materials: the supplied band is a flexible, durable elastomer similar to the material used in many sports watches. Other preserves that wording without guessing silicone, HNBR or fluoroelastomer.

Fluoroelastomer3Maker product pagemi.com/global/support/faq/details/KA-517264Read 15 October 2026Spec page names fluororubber straps for Black and Silver. Fluororubber is stored as fluoroelastomer.

Strap

Classic band2Maker product pagestore.google.com/us/product/fitbit_sense_2_specsRead 23 October 2026What's in the box: Classic band (Small and Large).

Fluororubber strap3Maker product pagemi.com/global/support/faq/details/KA-517264Read 15 October 2026Spec page strap rows for Black and Silver.

Strap sizesiPublished wrist-circumference range for the stated strap or case. Source notes distinguish an overall compatible wrist range from one supplied strap size.

AFitbit Sense 2

Size	Wrist (min) (mm)	Wrist (max) (mm)
Small	140	180
Large	180	220

Source1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Band size, printed page 63: Small band fits a wrist of 140 to 180 mm (5.5 to 7.1 in), Large band 180 to 220 mm (7.1 to 8.7 in). The Google Store page prints different ranges (130 to 180 mm and 165 to 220 mm). The manual is preferred. These are the supplied straps.

BXiaomi Watch S4

Size	Wrist (min) (mm)	Wrist (max) (mm)
Black fluororubber strap	140	210

Source1Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 2026The Black and Silver fluororubber straps have an adjustable length of 140-210 mm approx. The maker publishes strap length, stored as the wrist range. The Rainbow set with fluororubber and nylon straps is 135-210 mm.

Regulatory

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FCC ID

XRAFB5211Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026USA FCC statement: Model FB521, FCC ID XRAFB521.

Not available

SAR limb (US)iPublished limb/wrist SAR for the stated base regional model under the US regime. Other case sizes or radio versions can differ. Head or body SAR is excluded.

Not available

Not available

SAR limb (EU)iPublished limb/wrist SAR for the stated base regional model under the EU regime. Other case sizes or radio versions can differ. Head or body SAR is excluded.

Not available

0.232W/kg9Retailer pageteamplush.by/enRead 15 October 2026Same reseller copy: maximum SAR on the wrist 0.232 W/kg with no gap, against a 4.0 W/kg wrist limit averaged over 10 g, under the EU declaration. The near-mouth value of 0.132 W/kg is a body value and is not stored.

Other certifications

RED (2014/53/EU), UK Radio Equipment Regulations 2017, IEC 62368-1:2014, IEC 62368-1:2020 + A11:2020, ISED Canada (IC: 8542A-FB521)1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026EU section: Fitbit LLC declares Model FB521 compliant with Directive 2014/53/EU. UK section: Radio Equipment Regulations 2017. Safety Statement lists IEC 62368-1:2014 and IEC 62368-1:2020 + A11:2020. Canada section lists IC 8542A-FB521. These are model declarations, not medical, military or diving certifications.

EU RED 2014/53/EU conformity, RoHS 2011/65/EU conformity4Maker spec sheet (PDF)i02.appmifile.com/229_operatorx_operatorx_xm/29/08/2026/0506b1d933bea38854867532d7b1e253.pdfRead 15 October 2026The declaration covers RE Directive 2014/53/EU and RoHS Directive 2011/65/EU.

In the box

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In the box

Fitbit Sense 2, Classic band (small & large), Charging cable1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026What's in the box: watch with small band, charging cable and an additional large band.2Maker product pagestore.google.com/us/product/fitbit_sense_2_specsRead 23 October 2026What's in the box: Fitbit Sense 2 Classic band (Small and Large), charging cable.

Xiaomi Watch S4 (including bezel and strap), Magnetic charging dock, User manual (including warranty notice)1Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 2026Package contents row.

Power adapter in boxiA mains/USB power adapter is supplied. A charging cable, inductive puck or charging dock alone does not count.

No1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026What's in the box lists the watch, bands and the charging cable. No power adapter. The cable plugs into a USB port or a UL-certified USB wall charger.

No1Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 2026Package contents list only the watch, magnetic charging dock and manual. No power adapter.

Links

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Product page

store.google.com/us/product/fitbit_sense_23Maker product pagestore.google.com/us/product/fitbit_sense_2Read 23 October 2026Google Store product page for Fitbit Sense 2 (US).

www.mi.com/global/product/xiaomi-watch-s42Maker product pagemi.com/global/product/xiaomi-watch-s4Read 15 October 2026

Spec sheet

store.google.com/us/product/fitbit_sense_2_specs2Maker product pagestore.google.com/us/product/fitbit_sense_2_specsRead 23 October 2026This page is the maker's technical specs page for Sense 2.

www.mi.com/global/product/xiaomi-watch-s4/specs1Maker product pagemi.com/global/product/xiaomi-watch-s4/specsRead 15 October 2026Global specs page. Base case and strap describe the Black version.

Manual

storage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0d1Owner's manualstorage.googleapis.com/support-kms-prod/Cxknk8y9NHEphUUIYGTQvRVIFq1RZyQuGQ0dRead 23 October 2026Fitbit user manual, version 3.1, hosted on the Google Health Help Center user manuals page.

Not available

EPREL registration numberiId in the EU energy label database. Each size or model of a series has its own id, so it is per variant.

Not available

Not available

Warranty

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Manufacturer warranty (source market)iThe maker's warranty period for the exact SKU or configuration and market named in the source note. It applies only to that stated market, not every regional variant. Statutory consumer rights are excluded. The base term is stored. An extension that needs registration goes in the source note.

1year8Maker product pagesupport.google.com/product-documentation/answer/14815834Read 23 October 2026Fitbit Limited Warranty: new products carry one year from purchase, two years for EEA residents who bought in the EEA. Devices bought on or after July 11, 2023 fall under the Google Hardware Warranty Center terms. Stored as the US one-year term.

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Both are also in the API. Back to all smartwatches.