Xiaomi Watch S4 41mm Full Review: Premium Build, Serious Features
SmartwatchesKey Specifications at a Glance
The hardware facts that matter most, before the full breakdown.
Design and Build Quality
Size, Fit, and Everyday Wearability
At 41.2mm across and just 9.5mm thick, the Watch S4 sits in a genuinely versatile size bracket. It is compact enough that people with slimmer wrists won't feel overwhelmed, yet large enough that the display earns your attention. Weighing just 32 grams without a strap, this is a watch you forget you're wearing by midday — a meaningful quality for anyone who finds most smartwatches uncomfortably heavy during a full workday or overnight sleep session.
The AMOLED Display
The 1.32-inch AMOLED panel is one of the Watch S4's most compelling attributes. At 466 × 466 pixels across that screen size, the resulting 320 pixels per inch means text is sharp at a glance, watch face numerals render crisply, and health data charts read without squinting. AMOLED technology — which lights each pixel individually rather than using a backlight — delivers true blacks and vivid color saturation that makes any watch face feel premium.
Always-on display mode is included and fully functional. Knowing the time without raising your wrist or tapping the screen is a daily convenience that quickly becomes something you won't want to give up.
Sapphire Crystal Glass
The Watch S4 uses genuine sapphire crystal glass — not tempered glass, not Gorilla Glass — the same material found in watches costing significantly more. Sapphire ranks a 9 on the Mohs hardness scale, meaning it resists scratching from virtually everything encountered daily: keys, coins, concrete, brick surfaces. For a watch worn constantly, this is a compounding long-term advantage.
Replaceable Band
The band is fully replaceable using standard 20mm attachments — widely available and inexpensive. Swap materials, colors, and styles without hunting for proprietary accessories, keeping this watch from becoming disposable when you want a fresh look.
Water Resistance: Rated for Real Swimming
A 5 ATM water resistance rating means the Watch S4 has been tested to withstand pressure equivalent to 50 meters of water depth. In real-world terms: shower with it, swim in a pool or the ocean, and feel no concern about rain. The watch goes further than passive waterproofing — it actively counts swim strokes, recognizing your technique automatically during pool sessions.
One clear boundary: 5 ATM is not rated for scuba diving or high-velocity water activities like cliff jumping, and the watch is not designed for diving. For everything short of those extremes, it is capable and confident.
- Shower-safe
- Pool swimming
- Open-water swimming
- Active stroke counting
- Scuba diving (not rated)
- High-impact water sports
Performance and Core Health Tracking
The Watch S4 carries a complete sensor array. Here is what each measurement means for daily life.
The Full Sensor Suite
Advanced Metrics: HRV, VO2 Max, and Readiness
Three measurements separate casual fitness trackers from serious health tools — and the Watch S4 includes all three.
Heart Rate Variability
HRV measures the tiny time variations between each heartbeat. Higher HRV typically signals good recovery and cardiovascular health. The Watch S4 tracks this continuously, giving you recovery intelligence that was previously only accessible through dedicated lab monitors.
VO2 Max Tracking
VO2 Max is the gold-standard measure of aerobic fitness — how efficiently your body uses oxygen during intense effort. Tracking it over time reveals whether your fitness is improving, plateauing, or declining. This was previously a lab test; it now updates automatically during outdoor workouts.
Readiness Score
The watch synthesizes HRV, sleep quality, and activity history into a daily readiness score — a clear signal telling you whether your body is primed for a hard training session or needs a recovery day. This is genuinely actionable information, not a decorative metric.
GPS, Navigation, and Connectivity
Full GPS Independence
Built-in GPS means the Watch S4 tracks your outdoor routes, distances, and pace without a phone nearby. Adding Galileo — the European satellite system — expands the number of satellites the watch connects to simultaneously, improving accuracy in urban environments with tall buildings and in regions where GPS signal alone can be inconsistent.
Fast GPS acquisition minimizes the wait between pressing start and achieving a satellite lock. You are moving within seconds of beginning a workout, not standing on a corner waiting for a signal.
Route history and elevation tracking are both active, so post-workout you can review exactly where you went and how much you climbed — useful for runners, hikers, and cyclists analyzing their training patterns.
Cellular eSIM: Leave Your Phone at Home
The built-in eSIM slot connects the watch directly to a mobile network without your smartphone. This unlocks:
- Phone calls directly from the watch via the built-in microphone
- Text and app notifications received independently
- Music streaming to Bluetooth headphones without a phone
- Emergency contact when your phone is absent or out of battery
Bluetooth 5.4 and NFC
Bluetooth 5.4 is among the most current versions of the standard, delivering more stable headphone connections, faster pairing, and lower power draw than earlier Bluetooth versions. Built-in NFC adds contactless payments at any compatible terminal — tap your wrist at checkout without a wallet or phone.
Battery Life and Charging
Real-World Endurance
The Watch S4 is rated for approximately eight days between charges under typical conditions — meaning always-on display active for part of the day, continuous heart rate monitoring, sleep tracking, and moderate workout logging with GPS. For most people exercising once daily and wearing the watch casually the rest of the time, charging roughly once a week is a realistic expectation.
Heavy GPS use compresses this figure meaningfully. Long outdoor runs or extended hikes with GPS running continuously can bring a full charge closer to two to three days depending on total activity volume. Understanding this tradeoff before purchasing is important if your training involves daily multi-hour GPS sessions.
Wireless Charging
The Watch S4 charges wirelessly on a magnetic puck — no cable connected to a port. This is more convenient than fighting tiny proprietary connectors and eliminates port openings that could compromise water resistance over years of daily use.
Estimated battery by use pattern
Smart Features and Software
32GB Storage: A Genuine Differentiator
Most smartwatches offer little to no onboard music storage. 32GB is substantial — comfortably enough for thousands of songs. Combined with cellular connectivity and Bluetooth 5.4, the Watch S4 functions as a complete standalone music device during workouts. Download playlists to the watch, leave the phone at home, and stream audio to wireless earbuds directly from your wrist.
Voice Commands and Calls
The built-in microphone enables hands-free interaction — start workouts, set alarms, and manage the watch without touching the screen. The same microphone supports phone calls directly from the watch when paired with cellular, useful when your hands are occupied, sweaty from exercise, or gloved in winter.
Notifications and Smart Alerts
All wrist notifications arrive — calls, texts, calendar reminders, and app alerts. Call control is fully active: answer, decline, or manage calls from the watch face. A silent vibrating alarm wakes you without disturbing a partner. A remote camera shutter function lets you trigger your phone's camera from the watch — a small but genuinely useful feature for solo photography.
What the App Covers (Free & Ad-Free)
The companion app costs nothing and carries no advertisements. Full feature set:
Fitness Tracking
- Steps, distance, pace
- Calories burned
- Elevation tracking
- Exercise diary & tagging
- Activity reports & goals
- Swim stroke counting
Health Monitoring
- Sleep tracking & reports
- Body temperature trends
- Water intake logging
- Food & calorie tracking
- Weight tracking
- Menstrual & ovulation
Smart Features
- Calendar sync
- Music playback control
- Onboard maps
- Widgets & watch faces
- Inactivity alerts
- Fall detection alerts
Not Included
- Guided coaching plans
- Windows / Mac desktop app
- Turn-by-turn navigation
- ECG / AFib detection
- Wi-Fi direct connection
- No-account usage
Platform Compatibility
The Watch S4 pairs with both Android and iOS smartphones without feature gaps tied to phone platform — a deliberate design choice. iPhone users access the full feature set through Xiaomi's companion app on the App Store. This is worth flagging because some competing watches quietly reduce functionality for one platform over the other.
How It Compares to the Competition
The Watch S4 competes with Samsung Galaxy Watch, Amazfit's upper tier, and Garmin's entry-level sport line. Here is how the specifications stack up across the categories that matter most.
| Feature | Xiaomi Watch S4 41mm | Typical Mid-Range Rival | Typical Premium Rival |
|---|---|---|---|
| Display | 1.32" AMOLED, 320 ppi | AMOLED, similar size | AMOLED, similar size |
| Screen Protection | Sapphire Crystal | Gorilla Glass (typical) | Sapphire Crystal |
| Water Resistance | 5 ATM | 5 ATM | 5 ATM |
| Cellular (eSIM) | Sometimes | ||
| Onboard Storage | 32GB | 4–8GB typical | 16–32GB |
| GPS Systems | GPS + Galileo | GPS only (typical) | GPS + Galileo |
| HRV + VO2 Max | Varies by model | ||
| Battery (rated) | ~8 days | 5–7 days typical | 5–18 days (varies) |
| iOS & Android Support | Often Android-optimized | ||
| App Cost | Free & Ad-Free | Free (some paywalled) | Free or subscription |
Who Should Buy This Watch — and Who Shouldn't
Ideal Buyers
- Fitness-focused commuters who want to run or ride without their phone but stay reachable via cellular.
- Health-conscious everyday wearers who want HRV, SpO2, temperature, and readiness scores without paying flagship prices.
- iPhone and Android users equally — no platform gets a reduced experience.
- Swimmers and outdoor athletes who need real waterproofing and GPS route tracking.
- Display-quality-focused buyers — the sapphire AMOLED combination is genuinely premium at this tier.
- People with smaller wrists who find 45–47mm smartwatches too imposing.
Look Elsewhere If…
- You are a dedicated runner or triathlete who needs multi-band GPS, advanced training load analysis, or structured coaching built into the watch. Garmin's sport-focused lineup addresses those needs more completely.
- You are deep in the Apple ecosystem and want native watchOS, tight Apple Health integration, or Apple Pay specifically. Only the Apple Watch delivers that.
- ECG or irregular heart rhythm detection is a priority. The Watch S4 monitors heart rate thresholds but has no ECG sensor or AFib detection — meaningful for users with known cardiac history.
- You need offline turn-by-turn navigation. The watch has GPS and maps, but does not support pre-loaded route guidance during hikes or rides.
Honest Assessment
Where the Watch S4 Excels
Sapphire glass at this price point is unusual and sincerely appreciated — most competitors at the same tier use Gorilla Glass, which scratches more readily over months of daily wear. The 32GB of internal storage is a practical differentiator that transforms the watch into a viable standalone music device, not a spec-sheet talking point.
The display is among the better AMOLED panels in this size class — vivid, sharp, and power-efficient in always-on mode. Cellular independence, full cross-platform support, and a health sensor package covering virtually every metric a non-clinical user needs combine into a genuinely well-rounded package.
The companion app being both free and ad-free matters for long-term ownership. Many competitors lock advanced health insights behind monthly subscriptions — the Watch S4 gives you everything on day one at no ongoing cost.
Where It Falls Short
The absence of ECG functionality and irregular heart rhythm detection is a genuine gap. The watch alerts to high or low heart rate thresholds and tracks HRV, but it cannot produce a medical-grade electrocardiogram or flag atrial fibrillation — capabilities available on some competing platforms that matter meaningfully to health-motivated buyers with cardiac concerns.
No Wi-Fi direct connection is a practical limitation. The watch relies on Bluetooth to a paired phone or cellular for data — you cannot connect it to a home Wi-Fi network to manage the music library or download updates independently of your phone.
Coaching and guided training programs are absent from the software ecosystem. The app tracks, reports, and analyzes, but does not prescribe structured training plans. The one-year warranty period, while standard, is also shorter than some competitors offer at comparable price points.
Frequently Asked Questions
The questions real buyers search for before purchasing, answered directly.
Confident Recommendation
The Xiaomi Watch S4 41mm is a well-built, feature-complete smartwatch that punches above its price class in several meaningful areas — most notably its sapphire crystal display protection, 32GB music storage, cellular independence, and the quality of its AMOLED panel.
For the active professional, casual athlete, or health-conscious everyday wearer who wants a watch that can stand on its own without a phone and looks premium doing it, this is a strong and credible choice. It is not the right watch for someone who needs ECG monitoring, deep training analytics, or full Apple ecosystem integration — those are specific needs requiring specific tools. For everyone else, the Watch S4 41mm delivers genuine premium capabilities in a compact, lightweight package that most competitors at similar prices do not match feature-for-feature.
