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How to track sleep on a smartwatch or fitness tracker

By Christina Woodger

Could a smartwatch or fitness tracker improve your sleep? We explain how to track your sleep with a wearable, and share tips for sleeping better.

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Sleep-tracking is gaining in popularity, but how do you know if what your fitness tracker or smartwatch is telling you is accurate? 

We explain what to do with this data to get a better night's sleep, how apps can help, and offer tips on how to improve your sleep. 

In this article

Why is sleep important? 

Many of us routinely skimp on sleep - in fact, two thirds of adults throughout developed nations get less than eight hours sleep a night. 

You probably don't realise how sleep-deprived you are if you start each day with a strong coffee. Caffeine blocks sleepiness signals, artificially making you feel more alert. 

Insufficient sleep increases your risk of Alzheimer’s, cardiovascular disease, depression, diabetes, stroke and numerous other health problems. It shatters your immune system. And it interferes with hunger signals, too, increasing levels of a hormone that makes you feel hungry, while suppressing a companion hormone that makes you feel sated - which can lead to weight gain.

From a more cheerful perspective, getting the NHS-recommended seven to nine (on average eight) hours sleep - and making sure it’s good quality sleep -  is a free way to improve your health, memory, mood, appearance and decision-making. 

Can a wearable - a fitness tracker or smartwatch- help you sleep better? 

What do sleep-tracking wearables monitor? 

Not all fitness trackers and smartwatches track sleep, though the majority do now, and even cheap devices can offer some standard of tracking. Here's what you're likely to get:

Sleep duration - All sleep-tracking wearables will tell you, as a minimum, how long you've been asleep or awake. 

Sleep quality data - Many sleep trackers will also tell you whether your sleep has been restless or good quality. Some assign you a sleep score. 

Sleep stage data - Many sleep trackers claim to be able to tell you how long you spent in each stage of sleep (Light, Deep, REM, or Non-REM and REM). 

Sleep cycle alarm - Some will wake you up at the optimum point in your sleep cycle closest to the time you've requested. Whether or not you find this helpful will depend to some extent on your personality. A University of Bologna study of sleep cycle alarms on smartphones found that participants woke earlier than intended, and this may have been because they became anxious at the prospect of the early clock. 

Sleep problem detection - Some have the ability to detect sleep apnoea, a potentially serious health issue in which breathing stops and starts while you're asleep. It's important to note that these are not medical devices, so you shouldn't rely on them. If they do flag anything, though, you can take it up with your doctor. To be able to do this, a watch needs Pulse Ox, Pulse Oximetry or an SpO2 sensor (the ability to gauge the level of oxygen saturation in your blood - the name will depend on the brand). 

And some will give you tips for sleeping better, and act as a dashboard or journal so you can record factors that might be affecting your sleep, such as exercise and caffeine intake.

Do sleep-tracking wearables really work? 

Older and cheaper wristworn sleep-trackers rely on an accelerometer to auto-detect sleep. If you're inactive for a certain length of time, or your movements, such as rolling over, are considered to be typical sleep behaviour, then the tracker will assume you're sleeping. 

Newer models that can detect your heart rate and breathing are generally more accurate, as they have more data to go on. However, even these can incorrectly think you've been asleep when you've just been dozing on the sofa or that you've not slept at all because your sleep has been short. 

Many also claim to be able to track your stages of sleep (see the graph below). This is more of an estimate than something that should be viewed as scientifically accurate, though. Laboratory sleep-tracking - polysomnography - involves measuring electrical activity in the brain, breathing pattern, body position, snoring and more. Wearables simply aren't that advanced. 

Making data easily accessible

While wearables don't do a perfect job of recording your sleep times, they can present the data to you in an easily digestible format - graphs and charts through the companion app, for example. 

Plus, many offer extra features that can help you chart changes in your sleep over time and spot patterns so that, over time, you can build up a good picture of how your daily behaviours impact your sleep - and vice versa. And simply being more conscious of the need to get more sleep can encourage better sleep behaviour - which can, in turn, lead to better sleep.  

Don't get too concerned about the data from your smartwatch or fitness tracker, though. Dr Heather Morgan, lecturer in applied health sciences at the University of Aberdeen, and a specialist in digital health and fitness tracking, told us that wearables can help you better understand your sleep, and that analysing her own sleep had helped her achieve a better sleep pattern. 

'But', she adds, 'use your judgement and know your personality. If you're prone to anxiety, sleep tracking may not be for you. Trying to perfect your sleep could be one more thing to fixate on, which could, ironically, stop you sleeping'.

Which? tests of sleep-tracking wearables

We don't test how accurately a wearable can track sleep stages. However, for those that do offer sleep tracking, we look at how detailed and easy to understand the sleep data is and how plausible the sleep durations seem. 

If you do buy a wearable for sleep-tracking, make sure you pick one that's light and comfortable enough to keep on your wrist all night. There's no point buying one that's big and bulky, as you're simply not going to want to wear it. Bear in mind that fitness trackers are smaller and often more conformable to wear than smartwatches, so this might be a better bet, and use our fitness tracker reviews and smartwatch reviews to find a model that ticks the boxes.

What does a typical sleep-cycle look like? 

A typical night's sleep follows the pattern below, cycling through Stages 1 to REM every 90-110 minutes, with REM cycles getting longer each time. 

NREM (non-rapid eye movement sleep)

Stage 1 - light sleep

We drift in and out of sleep, our eyes move slowly and our muscle activity slows down. We are easily woken up again. 

Stage 2 - also fairly light sleep

Our bodies start preparing for deep sleep. Our eye movements, heart rate and brain waves slow down. Our body temperature drops. 

Stage 3 - deep sleep (sometimes you'll see this split into stages 3 and 4)

Deep sleep or slow wave sleep. Our heart rate and breathing rate are at their lowest, our muscles are relaxed and our brain waves slow down further. 

For healthy adults, 15-20% of your sleep should be deep sleep. 

We are difficult to rouse, and can feel disorientated if woken up from deep sleep. 

REM (rapid eye movement) sleep

We dream. Technically REM sleep isn't the only period of sleep in which we dream, but the vivid, hallucinogenic, often emotional, and bizarre experiences which seem to form a narrative come from REM sleep. 

Our eyes are closed but dart rapidly from side to side. Our brain activity returns to a more wakeful state. 

Our breathing becomes faster, irregular and shallow. 

Our limbs may become paralysed to stop us acting out our dreams. 

Interestingly, studies show that getting enough REM sleep helps us better read the social world around us. Insufficient REM sleep can, amongst other things, blunt our ability to discern changes in others' facial expressions and, thus, make it harder for us to navigate social situations. 

Some 20-25% of our sleep should be REM sleep.

How does my Apple Watch, Fitbit or Garmin track sleep? 

How the Apple Watch tracks sleep

Somewhat surprisingly, Apple doesn't have its own sleep app - not even on the latest Apple Watch, the Apple Watch Series 5, nor on the latest version of watchOS. 

You can still use your Apple Watch to track your sleep, using a third-party app such as Pillow, which you can download from the app store. Pillow is an iOS app only, so you can't use it if you're on Android. 

You can use Pillow on your iPhone instead of your watch, if you want to. If you use your watch, it will take heart-rate measurements into its calculations. If you use your phone in addition to or instead of your watch, it will use the phone's microphone to include analysis of your snoring; if you restrict access to the microphone, Pillow says its sleep analysis could be less accurate. 

The Apple Watch has a notoriously short battery, though; you'll likely need to charge it every night. So, if sleep-tracking is a priority for you, an Apple Watch isn't the best choice. 

Check out our Apple Watch reviews, or head to our guide on choosing the best Apple Watch, to see how Apple fares in other respects. 

How Fitbit tracks sleep

All Fitbit fitness trackers and smartwatches will track your sleep when you wear them to bed. After an hour of your body being immobile, your Fitbit will detect that you're asleep. 

Fitbits with heart-rate monitors, other than the Fitbit Surge and Fitbit Charge HR, are designed to track sleep stages. The Fitbit Inspire HR (£70) Fitbit Charge 3 (£90), Fitbit Versa 2 (£150) and Fitbit Versa (£120) are amongst the Fitbits which do this. They'll give you graphs and charts showing daily, weekly and monthly stats. Usefully, you can edit the times that have been recorded if you don't think they're correct. 

Some Fitbits, such as those in the Versa range, also have a sleep-cycle alarm, which Fitbit calls Smart Wake. 

Fitbits which don't track heart rate still show sleep patterns (time spent awake, restless and asleep) in the Fitbit app.

At time of writing, Fitbit is working on adding detection for sleep apnoea to some of its wearables. We'll update this guide when that feature becomes available. 

See all our reviews of Fitbit smartwatches and Fitbit trackers

How Garmin tracks sleep

Many Garmins - those with optical heart rate sensors - offer what Garmin calls Advanced Sleep Monitoring (ASM). 

These include the Garmin Fenix 5 and 6 series (of which we've tested the Garmin Fenix 5, £320), Garmin Fenix 5 Plus series (of which we've tested the Garmin Fenix 5s Plus, £420), Garmin Forerunner 45 (£132), Garmin Forerunner 645 (£386) and Garmin Forerunner 645 Music (£322), Garmin Forerunner 935 (£350), Garmin Venu (£290), Garmin Vivoactive 3 (£150), Garmin Vivosmart 4 (£76) and Garmin Vivosport (£90). 

Information you'll get includes estimates of your sleep stages, Pulse Ox and respiration rate. 

Garmin watches come packed with features for your daytime fitness needs too. You can read all our Garmin smartwatch reviews to find out more. 

Sleep-tracking rings 

If you don't fancy a wristworn wearable, another option is to buy a smart ring, of which there are a growing number on the market. 

Some of these focus on smart payments, but others, such as the Oura ring, from Finnish company Oura Health, are all about sleep.

It concentrates on two aspects of your health: rest and activity levels, but the main focus is on rest (especially sleep) on the basis that a good night’s sleep will help you perform at your best in all manner of ways in the day time. 

It uses pulse oximetry (monitoring the amount of oxygen carried in the body) and a 3D accelerometer and gyroscope to detect movement. And it collects data such as heart rate, heart-rate variability, calories burnt, body temperature, respiratory rate and steps and calories burnt, all of which you'll be able to see in the accompanying app. 

It's by no means a cheap option, though - the most basic version costs €314. 

Read our Oura ring review to find out what we thought of it.

Smartphone apps for sleep-tracking  

If you don't want a wearable at all, there are plenty of sleep-tracking smartphone apps you can use instead.

Smartphone apps rely on an accelerometer to detect movement and, by extension, sleep. So, even more than with wristworn devices, you can't expect them to track super accurately. 

Still, many offer useful tools - for example, playing 'dreamscapes' (music, voice overs and sound effects) to help you sleep better, giving you tips from sleep experts and teaching you cognitive techniques and behavioural strategies to reset your sleeping patterns. 

 The NHS recommends:

  • Pzizz - free for certain features, with the option to make in-app purchases
  • Sleepio - free in some areas of the country (currently Oxfordshire, Berkshire and Buckinghamshire)
  • Sleepstation - free with GP referral

How to sleep better 

You already know to avoid caffeine, phone and computer screens and heavy meals before bed. If you're still struggling to drift off despite that, though, here are some tips you might not have thought of. 

  • Stick to regular sleeping hours, even if you've had a bad night's sleep the night before. 'Catching up on sleep' is tempting, but can disrupt your routine.
  • Don't believe the myth that older people need less sleep. You may well struggle to get as much restorative sleep at night as you get older, due to the effect of medications, medical conditions and dozing during the day. But you should still be aiming for a full night's sleep of seven to nine hours. Sleep deprivation can be a factor in developing dementia. And the symptoms of sleep deprivation - depression, low energy, forgetfulness - can also be mistaken for dementia. 
  • Cut down on alcohol in the evenings. Although it is a depressant, and makes you feel drowsy, it increases your chances of waking up before you're fully rested. It also blocks REM sleep, meaning when you wake up you'll probably feel groggy. As a diuretic, it also makes it more likely you'll wake up in the night needing the bathroom. And it can lead to snoring - not ideal for anyone trying to get a peaceful night's sleep next to you.
  • Avoid cigarettes before bed, too. Smoking might help you relax, but nicotine is a stimulant that raises your alertness.
  • Understand your rhythm. There are biological and evolutionary reasons why some of us are owls and some are larks. If you're an owl forced into an early-to-bed routine for work reasons, don't add to your woes by beating yourself up if you can't fall asleep instantly. Try getting sunlight first thing - eating your breakfast near a window, for example - to reset your body's circadian clock. 
  • Make sure you're comfortable. Keep your bedroom dark and cool (16-18°C). Use our mattress reviews to buy a comfortable mattress, and review pillows regularly, replacing any that have gone lumpy.

Yoga can be a great way to relax and wind down. Read our guide on how to set up a home yoga studio to get started

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