Xiaomi Watch S4 Full Review: A Smartwatch That Earns Its Place

Xiaomi Watch S4 Full Review: A Smartwatch That Earns Its Place

Smartwatches
8.4
out of 10
Editor's Choice: Recommended
Battery
15 Days
Display
AMOLED
Water
5 ATM
Cellular
eSIM

Smartwatches have become crowded territory, and most of them blur together — same round face, same step counter, same vague promises about "smart health insights." The Xiaomi Watch S4 doesn't try to reinvent the category. Instead, it focuses on getting the fundamentals right: a sharp display you'll actually enjoy looking at, health sensors that go deeper than basic step counting, and a battery that doesn't demand a spot on your nightstand every single night. Whether that combination makes it the right watch for your wrist depends on what you're hoping to get out of it — and that's exactly what this review is here to settle.

15-Day Battery Life
Sapphire Crystal Glass
Built-in eSIM Calling
AMOLED Always-On Display
5 ATM Water Resistance
HRV & VO2 Max Tracking

Design, Build Quality, and How It Feels on the Wrist

At 47.3mm wide and just 12mm thick, the Xiaomi Watch S4 sits comfortably in the "noticeable but not bulky" category. It won't disappear under a shirt cuff, but it also won't feel like a dive computer strapped to your arm. Weighing in at 44.5 grams — lighter than a standard deck of playing cards — it's built for people who forget they're wearing it by the second hour, not the kind of heavy, tool-like watch that announces itself with every wrist movement.

The band is replaceable, which matters more than it sounds. Watch straps wear out, stretch, or simply stop matching your style after a while. Being able to swap it out means you're not locked into one look — or one fit — for the life of the device. A gym strap and a smarter option for the office can be the same watch, just with a 30-second band change between them.

Why the Sapphire Crystal Matters

The Xiaomi Watch S4 uses a sapphire crystal display cover rather than standard toughened glass. Sapphire crystal is prized in higher-end watches specifically because it resists scratching far better than standard glass — think of the difference between a screen that survives a drop on carpet versus one that survives years of contact with desks, doorframes, gym equipment, and car keys. For a watch brushing against surfaces dozens of times a day, that scratch resistance translates directly into a screen that still looks pristine long after a typical glass-covered watch would be showing hairline scuffs.

Comfort for All-Day and Overnight Wear

The compact profile pays off most during overnight wear. A watch that's too thick or heavy becomes an annoyance the moment you try to sleep in it, and since sleep tracking is one of this watch's core features, comfort during those eight hours isn't optional — it's a requirement for the feature to actually work the way it's meant to.

Physical Specifications
Dimensions47.3 × 47.3 × 12 mm
Weight44.5 g
CrystalSapphire Glass
BandReplaceable
Water Rating5 ATM / 50 m
Touch ScreenYes, full-touch

Display: Sharp, Bright, and Always On

The 1.43-inch AMOLED panel packs in a 466 × 466 pixel resolution — a density of 326 pixels per inch that puts it firmly in "you won't see individual pixels" territory, even with fine watch-face text and detailed complications. AMOLED technology means true blacks (because unlit pixels are genuinely off, not just dimmed) and vivid colors that don't wash out the way older LCD-based smartwatch displays sometimes do.

The Always-On Display is the feature that changes daily behaviour more than people expect. Instead of flicking your wrist or tapping the screen to check the time, the watch face stays visible at a dimmed brightness continuously. For anyone who's ever been mid-conversation or mid-meeting and didn't want the obvious "raise wrist and shake it" motion, this is the quiet, polite alternative.

1.43"
Screen Size
326
Pixels Per Inch
AMOLED
Display Technology
Always
On
Display Mode

Health and Fitness Tracking: The Real Reason to Buy

This is where the Xiaomi Watch S4 does its heaviest lifting. The sensor lineup — heart rate, blood oxygen, body temperature, accelerometer, gyroscope, compass, and barometer — works together rather than in isolation to build a genuinely comprehensive picture of your health and daily activity.

Heart Health, Around the Clock

Beyond a basic heart rate monitor, the watch tracks Heart Rate Variability (HRV) — the tiny fluctuations in time between heartbeats that can indicate how well your nervous system is recovering from stress, exercise, or poor sleep. Combined with resting heart rate tracking and a VO2 max estimate (a measure of how efficiently your body uses oxygen during exertion, used as a proxy for cardiovascular fitness), the watch builds toward a daily readiness score — a recovery indicator that tells you whether your body is primed for a hard workout or asking for a rest day.

Important Limitation: The Xiaomi Watch S4 does not include ECG functionality or irregular heart rate (AFib-style) alerts. If continuous arrhythmia screening is a primary reason you're shopping for a smartwatch — particularly for older users or anyone with a known heart condition — this is a meaningful gap compared to watches built specifically around cardiac monitoring.

Sleep, Recovery, and Readiness

Sleep tracking goes beyond "you slept for 7 hours 12 minutes." The watch generates full sleep reports, breaking down sleep stages and quality and feeding that data into the broader readiness score. One notable omission: there's no smart alarm — you get the sleep insights, but not the gentler wake-up feature that triggers during a lighter sleep phase. For a watch this focused on sleep data, that's a missed opportunity.

Workouts, Routes, and Everyday Activity

Step counting, distance tracking, pace measurement, elevation tracking, and automatic activity detection are all on board, alongside exercise tagging so your workout history stays organized. The route tracker records the GPS path of outdoor runs, hikes, or rides. GPS performance benefits from Galileo satellite system support plus a faster acquisition feature, meaning less standing around waiting for a lock when you start an outdoor session.

Cyclists should note the absence of ANT+ support — the wireless protocol used to connect external power meters and cadence sensors. There is also no built-in cadence sensor. Guided turn-by-turn route navigation is similarly absent: this watch tells you where you've been, not necessarily where to go next.

Swimming and Water Resistance

Rated for water resistance up to 50 metres (5 ATM), the watch handles swimming, showering, and rain without hesitation. It includes a stroke counter for tracking technique across laps. It is not designed for diving — the rating covers swimming and everyday water exposure, not the pressure demands of scuba or freediving.

Complete Sensor and Tracking Overview

Included in this watch
  • Continuous heart rate monitoring
  • Blood oxygen (SpO2) measurement
  • Body temperature sensor
  • HRV (Heart Rate Variability) tracking
  • VO2 max estimation
  • Daily readiness and recovery score
  • Sleep tracking with full stage reports
  • Automatic activity detection
  • GPS with Galileo satellite support
  • Route tracking and elevation recording
  • Swimming stroke counter
  • Fast and slow heart rate notifications
  • Fall detection
  • Barometer and compass
Not included
  • ECG / electrocardiogram
  • Irregular heart rate (AFib) detection
  • Smart alarm (wake during light sleep)
  • ANT+ accessory support
  • Built-in cadence sensor
  • Guided turn-by-turn route navigation
  • Perspiration monitoring
  • Dive-rated water resistance

Smart Features That Reduce Phone Dependency

Calling Without Your Phone: The eSIM Advantage

The standout feature on the spec sheet is a built-in cellular module with eSIM support. In plain terms, this means the watch can have its own phone number and data connection, independent of your phone being nearby. Leave your phone at home during a run and you can still receive and answer calls through the watch's built-in microphone and speaker. This is a tier of functionality usually reserved for more expensive smartwatches, and it fundamentally changes how "untethered" the watch can be during workouts, errands, or any situation where you'd rather not carry your phone.

Bluetooth 5.3

Offers a more stable, power-efficient link than older Bluetooth generations — fewer dropped connections and lower battery drain from the radio itself.

NFC for Payments

Hardware for contactless payments is built in. Availability of specific payment services depends on your region and bank support.

32GB Onboard Storage

Load music directly onto the watch and listen via Bluetooth headphones — no phone required during workouts.

Notifications and Alerts

Wrist notifications and vibrating alerts keep you informed without reaching for your phone. Silent alarm mode avoids waking a partner.

Voice Commands

Built-in microphone enables hands-free voice interactions and direct call handling from the watch face.

Remote Camera Shutter

Trigger your phone's camera from your wrist — ideal for group shots or self-timer photography where you need steady remote control.

Battery Life: How Long Will It Actually Last You

15
Days
Rated Battery Life

A 486mAh battery delivers a rated 15 days of battery life — well ahead of most smartwatches that demand daily or every-other-day charging. In practical terms, that's roughly two charging sessions per month instead of two per week. That reduction in "did I remember to charge it" mental overhead is more meaningful than it sounds, especially for anyone who wants sleep tracking to work consistently night after night.

Xiaomi Watch S415 days
Entry-Level Fitness Tracker7–10 days
Typical Mid-Range Smartwatch2–3 days

Charging is wireless — no alignment pins to fumble with, just set it on the puck. The battery is neither removable nor solar-assisted, which is standard for this category.

Companion App: Software That Powers the Hardware

The companion app is free to download and entirely ad-free — a detail worth appreciating, since plenty of fitness apps use ads or subscription paywalls to monetize free downloads. Both iOS and Android are supported, though there is no desktop version for Windows or Mac; all management happens through the mobile app.

Activity Reports
Daily summaries and trend data
Goal Setting
Customisable fitness targets
Achievements
Milestone badges for motivation
Calendar Sync
Workouts integrate with schedule
Maps and Routes
Review GPS paths after activities
Music Playback
Sync music for phone-free listening
Water and Weight
Log hydration and body weight
Women's Health
Cycle, period, and ovulation tracking

What's Missing From the App

There's no AI-driven coaching feature — meaning no adaptive training plans that adjust based on your performance and recovery data, a feature increasingly common in premium fitness watches. The app also doesn't support exporting reports to email, and there's no barcode scanner for quickly logging packaged food nutrition.

Using the app requires creating an account — there's no anonymous, account-free mode for privacy-conscious users. All management happens through the mobile app; there's no Windows or Mac compatibility for desktop users.

Who the Xiaomi Watch S4 Is Built For — and Who Should Look Elsewhere

Best Suited For
  • Runners, swimmers, and gym-goers who want serious activity tracking without a flagship price tag
  • Anyone tired of charging a smartwatch every night — the multi-week battery is a real quality-of-life upgrade
  • Phone-light users who want to leave their phone behind during workouts while staying reachable via eSIM
  • People who want women's health tracking integrated directly alongside fitness and sleep data
  • Buyers who want an Always-On AMOLED screen without sacrificing battery life to get it
Not the Right Fit For
  • Anyone whose primary need is cardiac health monitoring — no ECG and no AFib detection are real gaps
  • Serious cyclists with ANT+ setups (power meters, cadence sensors) that won't connect to this watch
  • Divers or anyone needing water resistance beyond swimming and showering
  • Users who want AI-guided coaching and adaptive training plans built into the experience
  • Apple ecosystem loyalists expecting deep native integration — Android users get the smoother experience

Competitive Positioning: How It Stacks Up

Rather than comparing against any single named rival, it's more useful to see where the Xiaomi Watch S4 lands relative to the broader categories it competes against. The watch punches above typical mid-range expectations while consciously skipping some expensive flagship-tier features to stay accessible.

Category Typical Strengths Where the Watch S4 Differs
Entry-Level Fitness Bands Lightweight, very affordable, basic step and heart rate tracking Far deeper health metrics — HRV, VO2 max, SpO2, body temperature — and a true AMOLED display rather than a stripped-down screen
Mid-Range Android Smartwatches Decent feature sets, but often 1–2 day battery life requiring frequent charging The 15-day battery and wireless charging meaningfully reduce daily maintenance compared to most watches in this tier
Premium Flagship Smartwatches ECG, cellular independence, advanced coaching, extensive third-party app ecosystems Matches cellular/eSIM independence but falls short on ECG, AFib detection, and AI coaching — strong value, not a full flagship replacement

Category Ratings Breakdown

Display Quality9.0 / 10
Battery Life9.5 / 10
Health Tracking8.0 / 10
Smart Features8.5 / 10
Build Quality8.5 / 10
Value for Money8.0 / 10

Honest Assessment: Strengths and Weaknesses

Where It Excels

The strongest argument for the Xiaomi Watch S4 is how rarely you'll think about it in a negative way day-to-day. The battery doesn't demand nightly attention, the display is genuinely pleasant to look at thanks to the AMOLED panel and Always-On functionality, and the sapphire crystal means the screen will likely still look pristine long after a typical glass-covered watch would be showing hairline scuffs.

The eSIM calling feature is the kind of thing that sounds like a minor bullet point until you actually use it — leaving your phone at home for a run and still being reachable is a small but real lifestyle upgrade. The health tracking suite is broad and genuinely useful, and the women's health tracking suite is a thoughtful, complete inclusion rather than an afterthought.

Where It Falls Short

The watch is not a clinical health monitoring device. The absence of ECG and irregular heart rate detection means it's not the right choice for someone specifically shopping for cardiac health screening tools. The absence of a smart alarm feels like an oversight given how much sleep data the watch already collects — the insight is there, but the most practical application of that insight isn't.

Cyclists with existing ANT+ hardware will need a different companion, and anyone hoping for AI-driven coaching will find the app capable but not adaptive. These aren't deal-breakers for the core audience, but they matter for anyone shopping with more specialised needs in mind.

Frequently Asked Questions

With a 5 ATM rating and 50-metre water resistance depth, it's built to handle swimming, showering, and general water exposure without issue. It is not rated or designed for diving.

To a meaningful degree, yes. The built-in eSIM and cellular module allow it to make and receive calls independently. Full app functionality and detailed syncing still rely on a paired phone when available.

Yes — call control and the ability to answer calls are built in, supported by an onboard microphone and speaker. This works either independently via eSIM or through a connected phone via Bluetooth.

Both. The watch and its companion app support iOS and Android. That said, Android users will typically get the more complete and integrated experience, as is common with non-Apple smartwatches.

The rated battery life is 15 days, well above the daily or every-other-day cycle common to most smartwatches. Charging is wireless — no alignment pins, just set it on the charging puck.

No. The Xiaomi Watch S4 includes heart rate monitoring, HRV tracking, and resting heart rate data, but it does not include ECG functionality or irregular heart rate (AFib-style) alerts.

Yes, the companion app is free to download and entirely ad-free. Creating an account is required — there is no anonymous, account-free mode.

The Xiaomi Watch S4 comes with a standard one-year warranty from the manufacturer.
8.4
out of 10
Recommended

Final Verdict: Should You Buy the Xiaomi Watch S4?

The Xiaomi Watch S4 earns its place by doing the unglamorous things exceptionally well: a battery that lasts weeks instead of days, a display that's genuinely satisfying to glance at dozens of times a day, and health tracking that goes meaningfully deeper than step counts and calorie estimates. The eSIM calling capability alone sets it apart from most watches in its tier, offering phone-free independence usually reserved for far pricier devices.

It's not trying to be a clinical health monitoring device — skip it if ECG and arrhythmia detection are non-negotiable for you — and serious cyclists with ANT+ hardware will need a different companion. But for the much larger audience of runners, swimmers, gym regulars, and anyone who wants serious fitness and wellness tracking without babysitting a battery every night, the Xiaomi Watch S4 is a confident, well-rounded recommendation.

15-Day Battery Sapphire Crystal eSIM Calling AMOLED Always-On HRV & VO2 Max Free & Ad-Free App

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