Xiaomi Watch S4 Review

Introduction

The Xiaomi Watch S4 swings in to update the Watch S3 from 2024. Regular as clockwork, the Watch S4 returns with some of the features of its forebear while making a few updates, too. 

At its core, the Watch S4 is a similar proposition to what came before. Focusing on value for money, this isn’t a watch that competes with the likes of the OnePlus Watch 3 and the universality of Wear OS. Instead, it looks to offer a fairly broad set of smartwatch features without overcomplicating things. 

Priced at £129.99, it’s typical of the affordable end of the smartwatch scale. For some, it will do everything you want it to. The question is, how well does it do it?

Design and Screen

• Removable bezel
• New rotating crown
• 1.43-inch AMOLED display

The Xiaomi Watch S4 looks like the previous iteration, but there’s now a rotating crown, which brings a touch of class to this affordable model. The highlight feature of the Watch S4 is the removable bezel, meaning you can twist it off and change the look, perhaps to move from a sporty aesthetic to something more formal. 

That’s easy enough to do. The watch comes in three colours – silver, Black (on review here), and Rainbow, which has a slightly more premium strap with colour highlights and a bezel that’s a little more interesting – but it does cost £10 more.

The Watch S4 has an aluminium alloy frame, which is round, 12mm thick, and measures 47.3mm across; it weighs 44.5g. It’s a fairly generic look and there’s little embellishing the design, leaving it to that rotating crown and changeable bezel to add interest.

The strap is a fluororubber affair, pretty easy to switch thanks to the spring pins on the rear. It’s a slight oddity in that you tuck the loose end of the strap back inside it once buckled, so I’m forever putting it on and having to loosen it to fit the strap in. It’s tidy and saves flapping around but it’s a bit of a faff. 

Xiaomi wants you to switch up the straps and sells bezel and strap kits, some of which have exclusive watch faces, making them feel a little more special. They are priced between £24.99 and £34.99 – and that includes various leather straps, ceramic and carbon bezels, so it’s a cheap way to upgrade the look of your watch. 

There’s a 1.43-inch display on the Xiaomi Watch S4 and Xiaomi is keen to point out that it’s really bright. That’s perhaps a strange flex, as out of the box, the Watch S4 is keen to dim the display as quickly as possible, always-on is off by default, as is raise to wake. It takes a bit of digging around to get it showing you information easily and it even turns off when exercising, so you’ll have to turn that on too.

It’s also a reasonable-quality AMOLED display with a 466 x 466 pixel resolution (326ppi) and a peak brightness of 2200 nits. That’s as bright as the OnePlus Watch 3, and I found it perfectly bright enough in direct sunlight. It’s a 60Hz display. 

There’s nice vibrancy to the colours as you’d expect from an AMOLED display and I found the graphics to be sharp enough to see what was going on without any problems.

Performance and Software

• HyperOS 2
• Works with Android and iPhone
• Xiaomi phone owners get some advantages

Xiaomi doesn’t declare what powers the Watch S4, but unlike a smartphone, that’s not hugely important.

What’s more important is that this watch skips around its user interface without lag or delay, although I did find the icons to the far left of the screen sometimes a little reluctant to respond compared to those in the centre of the display. This is likely because of some touch confusion between those apps and the swipe gesture to navigate back, which you’d trigger from the same place. 

This watch runs Hyper OS 2, which is the same name as the software that runs on Xiaomi’s latest phones, like the Xiaomi 15, but whereas the phone version is an Android skin, it’s not clear if that’s the case on the Watch S4. It’s a proprietary operating system from Xiaomi on the watch, and you can’t use it like a Wear OS watch. 

That means you need to use the Mi Fitness app on your phone to connect and control it, with everything routing through that. It also means there’s no access to AI assistants and the app selection is limited to what’s on the watch. 

Those apps cover the main watch functions giving you lots of faces, mobile payments, music support, alarms, tasks, weather, contacts, as well as exercise tracking, sleep tracking, voice recorder, calendar, remote camera trigger and a collection of other wellness functions. 

That all sounds great, but there’s a lot to break down here: many of these functions need priming by Mi Fitness on your phone first. For example, contacts don’t automatically sync, you need to manually add them. Music doesn’t sync to any service, it wants to use downloaded tracks from your phone. There’s no Spotify playlist syncing here.

The mobile payments list two supported banks: Curve and ZEN.com. You can’t just add your card and get spending, so there are some hoops to jump through to get it working. 

But I did find that the remote trigger for the camera worked well enough with the Samsung phone I tested the watch with, as well as a Xiaomi phone. The calling also works, but it’s a bit of a novelty feature. The speakers are surprisingly good, however, should you ever need to use that function.

There is a preference for Xiaomi phones too. I found that the calendar syncing only worked when connected to a Xiaomi phone, while you can also control smart home devices from the Watch when you’re connected to a Xiaomi phone. I didn’t test this last function, however, because I didn’t have any compatible smart home devices.

You’ll also find that do not disturb on your phone syncs to the watch to silence notifications, and vice versa, so turning on DND on your watch will also turn it on for your phone.

Health and Sleep Tracking

• One tap health checkup
• Easy to scroll through wellness cards
• Sleep, stress and relaxation included

Many people turn to wearables for the health monitoring functions they offer, combined with exercise tracking. These two elements of a smartwatch go hand-in-hand, with things like daily activity monitoring and steps falling more on the health side than the exercise. 

This is core to the Xiaomi S4’s offering, with the heart rate sensor on the back doing its part to monitor you 24/7. Tapping on the checkup will run a 60-second health check that looks at your heart rate, your oxygen saturation, stress and sleep stats. I found it said that everything was “ideal”. Honestly, it’s hard to decide if it’s a useful feature or not. 

Twisting the new crown will flick through cards on the screen showing some of your vitals, including your heart rate, activity stats, and sleep with the weather thrown in for good measure.

Sleep tracking has seen a huge boom in recent years, with many people able to access wearables to give some guidance as to just how good or bad their sleep was. Yes, if you sleep badly, you probably know all about it as you drag yourself out of bed, but with the Watch S4, you’ll get a little feedback to guide you. It said I go to bed too late, which is fair.

Xiaomi then tracks your sleep stages through light, deep, and REM, assigning you a sleep score and telling you what sleep animal you are. If that sounds familiar, that’s because Fitbit and Samsung also do that. But Fitbit also tells you your awake time, which Xiaomi seems a little less likely to report. 

That led to different sleep times being recorded by the Fitbit Charge 6 I wore at the same time: that would tell me I was awake for 1 hour of the night, whereas Xiaomi seemed to credit me with a lot more deep sleep. Both agreed on the REM times. Which is more accurate? That’s a hard call, but I found awake time to be much rarer from the Xiaomi watch.

There’s also stress tracking and an app to guide you through relaxing breathing. The breathing guidance is accompanied by haptics and audio from the Watch S4 which, quite frankly, was anything but relaxing. Again, there’s nothing really unique about this offering, it’s now common on many wearable devices, but completes the wellbeing feature set.

Exercise Tracking

• 150 exercises – including “esports”
• Heart rate tracking can be a bit wayward
• Strava and other app connections

Exercise tracking was probably on your mind when you first started thinking about the Xiaomi Watch S4, as this is now an obligatory feature of any bit of wearable tech. This watch is certainly cheaper than the best Garmin watches, and with 150 activities to track, you might find it will do the job for you. 

Those activities include everything from the regular running, walking, cycling and swimming, to the bizarre, such as darts and esports – as well as everything else you can imagine. Importantly, if you’re skiing and want to record something as skiing, you can, and that’s the point. 

What’s more, if you are skiing and it detects a fall, if you don’t respond within 60 seconds, it will call your emergency contact, which is a neat little safety feature.

There’s no mapping on the Watch S4 itself, but I found the GPS route it recorded in the app to be accurate compared to my Garmin Fenix 6 Pro and when compared to the GPS on my Hammerhead Karoo 2 bike computer. That means distance, speed and pace generally seem to be accurate. 

Heart rate can be a bit variable: I found the averages were generally in the right place, but often I’d glance and see that it was tracking at somewhere over 160bpm, which felt about 20bpm higher than it should be.

What this all amounts to is a watch that’s accurate enough (but with some foibles), while also throwing in some advanced features like vertical amplitude and ground contact time, which are more advanced metrics for runners. 

You also get a readout of the training effect, so you can get a measure of the intensity and whether you need to back off a bit. It’s a fairly comprehensive offering, which is great on a device that’s such good value for money. 

Taking things further, there’s the option to sync with Strava, Health Connect and Suunto. That gives more options for compiling and analysing your data across devices, so it doesn’t end up siloed in Mi Fitness for the rest of time – and that’s very welcome. 

There’s also an auto function for activities, which I found would occasionally pop up to tell me that I was going for a walk. This is nice and convenient for casual exercise.

I found the Xiaomi Watch S4 to be fairly complementary: it said I slept better than most people my age and that I was an “athlete” based on my running ability. I doubt both of those statements, but if a £129 watch is going to resort to flattery, then I’ll happily accept it.

Battery Life

• 15-day battery life
• 486mAh battery
• Fast charging

Let’s face it: smartwatches got a bad reputation when Apple Watch normalised charging every night. Meanwhile, the likes of Garmin offer two weeks on a single charge, setting a different expectation. It’s fitting then that Xiaomi continues to offer up to 15 days of life from a single charge on the Watch S4. 

But that comes with a caveat: use the always-on display or track your exercise, and that number will quickly start to drop. Even so, I’ve found it lasted for a week even with a couple of runs tracked and changing the settings so the display isn’t constantly off.

There’s a charger in the box with contact pins, so it’s not a standard wireless charging option. The advantage of this bespoke charger is that you can get a couple of days of use from it after only five minutes on the charger – however, don’t expect that to be two days where you’re logging exercise sessions!

Ultimately, the battery life on the Watch S4 wasn’t a concern. It’s a solid offering from a smartwatch, meaning you can wear it 24/7 without worrying that it’s going to die after two days.

Should you buy it?

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