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Updated: 1 Jun 2022

How we test smartwatches

From battery life to notifications and fitness tracking accuracy, we test it all so you can pick the perfect smartwatch for you.
Rebecca Jakeman
Smartwatch music_advice 486753

It isn't easy for a smartwatch to earn our Best Buy recommendation – we only recommend models that offer genuine benefits above and beyond simply using your smartphone alone. 

If a smartwatch is difficult to use, uncomfortable to wear, lacks important features and needs constant charging, you may well find you never wear it. 

Smartwatches from all the big brands, including Apple, Fitbit, Garmin, Huawei and Samsung go through a raft of tests both in and out of our lab. The very best smartwatches will have brilliantly clear and reactive screens and plenty of useful smart features – and be able to track your activity accurately, too. 

To find out which models aced our tough tests, head over to our round-up of the best smartwatches

Smart features

Smartwatches all receive text messages, call notifications and calendar alerts, and most receive email and social media notifications, too.

But we’ve found differences in the level of detail you can see and how easy these notifications are to view. Some simply tell you that you've received a notification, so you’ll have to dig around for your phone to find out exactly what’s happening, whereas others make it easy to reply and even allow you to make calls directly from the watch.

And many give you the option to filter which notifications get pushed from your phone to the smartwatch, whereas it's all or nothing with others. 

Many offer music control, so you can listen via Bluetooth headphones while out and about, or use your watch to control music playing from your smartphone. In other cases, you can store music directly on the watch or stream music from services such as Spotify. 

Some smartwatches have great accompanying apps that are easy to navigate and offer useful, detailed information. Others are clunky, hard to find your way around or slow to update. 

Our expert testers compare the smart features of each smartwatch, as well as any annoying niggles. We also test how reliably each smartwatch receives notifications from your smartphone by checking if all alerts are received. 

All of this will help you to decide whether it’s worth forking out hundreds for a smartwatch, or whether you’re better off just using your phone.

Settings and customisation

Everyone's different, and smartwatches need to be able to adapt to give you the features you need the most. Maybe aesthetics are important to you, or you want plenty of choices of watch face to suit the occasion. 

Or maybe you want the option to be able to download third-party apps for more advanced fitness tracking, or for adding extra features and functions. 

We delve into the settings of each watch, and their accompanying smartphone apps, to find out which are the most versatile and most capable of being tailored to do exactly what you need them to. 

Battery life

If your smartwatch takes hours to charge up, you'll probably find yourself often leaving home without it. And if it doesn’t last long enough on each charge, you’ll fall out of love with your watch quite quickly.

In our lab we check how long it takes for the smartwatch battery to charge from dead to 100%. The best charge in less than an hour, while the worst take more than three hours. 

We also check how much battery life you'll get from a 30 minute charging session – useful if you only realise it's dead when you wake up in the morning, for example, and want to give it a quick burst before heading off to work. 

And of course we also test how long the fully charged battery will last by putting each device through a series of tests – we replicate typical daytime and nightime scenarios both in and out of our lab, including sending two phone calls and 35 messages to the phone linked to the watch. 

Screen quality and scratch resistance

The best smartwatches are designed to be worn day in, day out. But that means these pricey devices could be put through all sorts of situations – whether that’s hopping on and off public transport, wearing it during a difficult workout session, doing a bit of DIY or for hiking over tough terrain. 

So your device needs to be comfortable, well-built and suitable for both indoors and outdoors use. 

Our reviews can tell you if the watch seems solid and durable, based on the materials it's made from. Some look strong and sturdy – or glamorous and premium – in the PR photos, but appear much more cheap and flimsy up close. 

We can also tell you whether the screen is clear, bright and high-resolution and easily readable in dark and low light, and how easy it is to wake up so you can quickly tell the time.

Scratch resistance gets a workout too with a dedicated scratch-test tool, which applies a set force to the watch. These are pricey devices, so you don't want to end up with unsightly marks on the screen. 

Fitness-tracking accuracy

Many smartwatches include a variety of sensors to capture your fitness data. Some – which are also called fitness watches or sports watches – are specifically targeted at exercise enthusiasts, and come packed with fitness tracking capabilities. Even those that are more about fashion and staying connected will generally track things like your steps, number of floors climbed, heart rate and, increasingly, aspects of your sleep. 

Seeing your activity – or how inactive you’ve really been – right there on your wrist can be a great motivator to exercise more. But only if you can rely on the readings your smartwatch provides, which is why we check the accuracy of the fitness functions of each device.

Our reviews can give you information such as:

  • how accurately a smartwatch tracks the number of steps you've taken
  • whether a smartwatch tracks your distance travelled using GPS (which often makes it more accurate) or using your step count
  • if it has heart-rate tracking, and whether it can track your heart rate accurately

To measure steps, for example, our testers go on a 10 minute walk and a 10 minute run, and take part in a range of household activities, including sitting reading a magazine, packing and unpacking a dishwasher, sweeping the floor, going up and down stairs and carrying shopping bags. We compare the smartwatch data to a trusted reference step counter. 

For measuring distance, we walk and run routes with known distances and check if the smartwatch can accurately tell us how far we've travelled. Our walking and running routes include woodland areas, giving GPS watches more of a challenge. 

To measure heart rate, we test a smartwatch during low and high intensity running, and while resting. If the watch struggles – gives no heart-rate data or really abnormal heart-rate data, say – we take a second reading. We compare results to chest belts, as reference devices, which use an electrical measurement method that is known to be more reliable – so we know we can trust their data. 

73% The score a smartwatch needs to earn to be considered as a Which? Best Buy

Blood oxygen (aka pulse oximetry or SpO2) monitoring

An increasing number of wearables can monitor your blood oxygen saturation: the amount of oxygen being carried around your system by your blood cells, expressed as a percentage. 

Some smartwatches and fitness trackers are able to do this on-demand, some work overnight, taking readings while you sleep, and some can do both. 

If a wearable can take an on-demand blood oxygen measurement, we test how accurate the measurements are, compared to those taken by a medical pulse oximeter that we use as a reference device. 

We test this on 10 healthy people (five men and five women) whose blood oxygen levels are within the normal range. 

We don't factor this into our test score, as it's not a feature that most people need. However, we can tell you whether it falls within the threshold of accuracy tolerated by the FDA (US Food and Drug Administration). There's no UK or EU standard for pulse oximetry features on wearable devices at the moment, unlike medical grade pulse oximeters. 

As our blood oxygen testers come from a range of ethnicities, we can also tell you if we find differences in accuracy on different skin tones. Due to the technology involved, some wearables work on very pale white skin but give inaccurate results, or don't work at all, on darker skin, for example. 

Even if a wearable can take accurate pulse oximetry measurements, it's important to remember that our testers are healthy people and that these watches and trackers aren't intended to be medical devices. Therefore, you shouldn't rely on a wearable to detect signs of a medical condition. Medical pulse oximeters are being used for remote monitoring of patients with Covid-19, but pulse oximetry features on wearables are intended for what manufacturers call 'recreational' use only. In other words, they're more like toys for people who are generally healthy and want to learn more about their bodies. Follow the latest NHS guidance to stay safe from Covid-19, and seek medical help if you become concerned about your health. 

On-demand pulse oximetry data is probably most useful to hardcore athletes and alpinists, who might be at risk of over-exertion. If your blood oxygen levels dip while you're working out or climbing, it might be a sign that you should take a rest. 

If you notice any unusual measurements in your overnight pulse oximetry measurements, it could be a sign of sleep apnoea, a sleep disorder in which your breathing stops and starts. Again, don't take this as a diagnosis: raise it with your GP. 

Are the smartwatches secure?

We put every smartwatch we review through a privacy and security test to check for vulnerabilities that could be exploited by unauthorised parties.  

It's probably hard to imagine anyone wanting to hack your smartwatch. But wearable devices can gather plenty of sensitive personal information about you beyond your calorie burn and how many steps you've clocked up: where you are, what time you go to bed, maybe even your ovulation cycle – and this information could attract the attention of would-be thieves and hackers.

In 2017, we reported on an investigation by the Norwegian Consumer Council (NCC) that found children’s smartwatches vulnerable to hackers. 

An insecure smartwatch could also act as an entry point to your home network, jeopardising the security of laptops, phones and other devices which hold even more information about you. 

Data encryption

Our test looks at whether your personal data is encrypted: scrambled, so that others can't read it. We also check where your data is being sent, particularly if that’s outside of the EEA (European Economic Area). 


If firmware (the software programmed into your smartwatch) isn't maintained, it can leave holes through which a hacker could access your smartwatch. Will the manufacturer continue to develop updates for your smartwatch, and for how long?

Data transparency (permissions)

Can you opt out of individual data permissions? If you do, what's the impact? We check what data the app is asking for, and the reasons behind it, to make sure data isn't being collected for the sake of it. 

Password policy

We check whether smartwatches oblige you to set passwords that aren't easily cracked. We also look to see whether there’s any option to access your account using biometric methods, such as Face ID or a fingerprint. Our guide explains more about setting a secure password.


If the smartwatch has wi-fi connectivity, we test to see if it can join a wi-fi network that isn’t secure.

Man-in-the-middle attacks

We check if smartwatches are susceptible to a 'man-in-the-middle' attack. This is where a third party intercepts data being sent to and from your smartwatch. 


The market for second hand smartwatches is growing – which is a good thing from an environmental perspective. If you buy a second-hand smartwatch, you'll want to be sure that it's fit for sale, and that none of the old user's data is still attached to it. If you sell or donate yours, you should be able to remove your data via a factory reset. 

New forms of cyberthreat

The threats posed by hackers are constantly changing, so we’ll update our review process as new threats emerge.

There’s no such thing as total security when it comes to connected devices. But we check for the most common attack vectors, and alert manufacturers to any issues we find. The wearables that we recommend had nothing that worried us at time of testing. 

If a wearable can be used by both Android and iPhone users (most of them can), we test both the Android and iOS versions of the app.

We’ve reviewed most of the wearables that you’re likely to see on sale from popular brands. If you buy a wearable that we haven’t tested, we'd advise sticking to popular brands. A big name is no guarantee of good quality – as our testing has shown time and again. But a well-respected brand is much less likely to risk its good reputation by being careless when it comes to privacy and security. 

Should I buy it?

Each of our assessments goes some way to making up a smartwatch total test score.

Some factors are more important than others, so we weight each result to ensure that the smartwatch features you’re likely to use most are the ones that contribute the highest proportions to the total test score. 

The score is broken down as follows:

  • 25% smart features
  • 25% fitness features
  • 20% ease of use
  • 15% battery
  • 5% quality of the accompanying app
  • 5% build quality
  • 5% features

A smartwatch needs to score at least 73% in our tests to earn our Best Buy recommendation. 

Make sure you don't spend your money on an inaccurate, uncomfortable and clunky smartwatch. Use our smartwatch reviews to find your perfect model.