What is sleep tracking, how does it work and what devices offer it?

Sleep tracking has been around for several years, with numerous companies and devices offering it - some in more detail than others and some providing more useful data than others.

It involves tracking sleep stages, typically categorised as light, deep and REM (rapid eye movement or dreaming), with a breakdown of how long you were in each stage, and your sleep duration over the night. 

There are dedicated sleep tracking devices, as well as fitness trackers and wearable devices capable of tracking your sleep - but the data delivered and features offered vary between devices and companies. 

Some companies offer sleep scores, some have smart alarms to wake you up within a set window when you're in the lightest sleep and others combine your activity and sleep data to give you an insight into your overall recharging and what you need to do for the best results. 

Here's everything you need to know about sleep tracking and which companies offer what. 

How does sleep tracking work?

Sleep studies performed in a lab uses polysomnography, measuring brain activity, eye movements and body movement through sensors attached to your head. In order to classify sleep into stages, the variation in the heart's beat-to-beat intervals has to be measured and it's said that a sleep technician should measure signals in 30-second epochs.

Of course, wearables and sleep mats don't have the luxury of a lab and sensors attached to your head - and neither would you want that every night. Instead, sleep tracking with these devices is done by using the heart rate monitor and motion sensors to detect which stage of sleep your body is in during the night. Throughout the night, your body will dip in and out of the different stages: awake, light, deep and REM.

Your body needs a combination of all these stages to recover, rebuild and leave you feeling rested when you wake up. Light is said to strengthen memory and learning, while deep helps with physical recovery and REM is said to help with strategic thinking and creativity.

Why are people so interested in sleep tracking?

There have been lots of studies that link good quality sleep to a healthy lifestyle. Proper sleep can lower your stress levels, lower blood pressure, help your immune system stay strong, and help you recover mentally and physically from the stresses on your body. 

Good sleep helps you stay sharp mentally - important for those in education or in mentally taxing jobs - as well as physically strong.

Sleep is particularly important for physical recovery from exercise and for many athletes, it's an important part of a training regime. It's through recovery - including sleep - that you rebuild the muscles and systems you have stressed, making yourself stronger.

What devices offer sleep tracking?

Here is a breakdown of the companies and devices that offer sleep tracking and the different features offered.

Fitbit 

All of Fitbit's wrist-worn activity trackers offer automatic sleep tracking when you wear them to bed. The heart rate monitor - if your device has one - combined with the motion sensors tracks your sleep and provides you with a breakdown of your sleep stages and a Sleep Score out of 100 when you wake up to help you gauge how well you have slept.

In the Fitbit app, you can see your sleep trends over time and you'll be provided with insights to help you better understand your night's sleep, though the insights aren't as useful as Garmin's Body Battery.

All Fitbit's latest devices offer silent alarms - waking you up with a gentle vibration on your wrist. Some Fitbit devices - those with heart rate monitors - also have Smart Wake, with the device waking you up during the optimal stage of sleep within a window set by you.

Fitbit devices offering sleep tracking include: 

• Fitbit Inspire HR
• Fitbit Charge 3
• Fitbit Charge 4
• Fitbit Versa
• Fitbit Versa 2
• Fitbit Versa Lite
• Fitbit Ionic

Withings

Withings offers sleep tracking through its wrist-worn activity trackers but it also offers a dedicated sleep tracking mat - Sleep Analyzer - that is placed under the mattress meaning you don't have to wear anything to bed. 

The Sleep Analyzer offers sleep stage data and a sleep score but it also has sleep apnea detection by measuring your breathing, heart rate and body movements, as well as snore detection. 

The Withings activity trackers automatically track your sleep when worn to bed, offering a Sleep Score, as well as light and deep sleep stages, silent alarm and Smart Wake-Up features, much like Fitbit but without as much data.

Withings devices offering sleep tracking include:

• Withings Sleep Analyzer
• Withings Move ECG
• Withings Steel HR
• Withings Scan Watch
• Withings Pulse HR

Polar

Polar's most advanced level of sleep tracking is called Polar Sleep Plus Stages and it automatically tracks the amount of sleep you've had, along with the quality and tells you the duration of time spent in each sleep stage. There's a sleep score out of 100 - broken into a reflection of solidity, quantity and regeneration. 

There are insights so you can see how various components of your sleep score compare to your usual level. Separately, Polar also offers something called Nightly Recharge. This takes the sleep data and sets it in the context of your daily activity to see how well recharged you are. A heavy training day followed by poor sleep and you'll be advised to rest rather than train. 

The following Polar devices offer the company's Sleep Plus Stages, with Nightly Recharge: 

• Polar Vantage V Titan
• Polar Vantage V
• Polar Vantage M
• Polar Grit X
• Polar Ignite
• Polar Unite

Garmin

Garmin has a comprehensive sleep tracking suite that again will track your sleep stages and present you with a picture of how you slept. As many Garmin devices will also give you oxygen saturation readings, this also forms part of the sleep score, along with your respiration level. 

The data flows into a system called Body Battery which takes into account your stress and activity levels from the day before to reflect how well recovered you are. It's a superb system and it really works, giving you an idea of how much you have in the tank.

Sleep tracking is widely supported by Garmin devices. Below is a list of more recent devices that also offer Body Battery:

• Garmin Approach S62
• Garmin Fenix 6 series
• Garmin Forerunner 245 / 245 Music
• Garmin Forerunner 45 / 45S
• Garmin Forerunner 945
• Garmin Swim 2
• Garmin Instinct
• Garmin Instinct Tactical
• Garmin Legacy Hero and Saga series
• Garmin MARQ series
• Garmin Quatix 6
• Garmin Tactix Delta
• Garmin Venu
• Garmin Vivoactive 4 / 4S
• Garmin Vivosmart 4
• Garmin Vivomove 3 / 3S
• Garmin Vivomove Luxe
• Garmin Vivomove Style

Samsung

Samsung uses a combination of heart rate and movement during the night to determine how well you've slept. If you're wearing one of its compatible watches of fitness trackers, it'll automatically create a chart for you to view the next morning when you wake up. 

Within this graph you'll see how many hours you spent in deep sleep, light sleep and REM sleep, with a breakdown beneath that chart showing you how that compares to the optimal time in each sleep cycle. It then uses this data to create a sleep score out of 100. The higher the sleep score, the better sleep you had. 

Once you've tracked a few nights sleep, Samsung Health (the app that you use to keep track of it all) will create an average breakdown for you and help understand how to improve your sleep by telling you to stop going to bed too late, or aim for a consistent bedtime every day.

Most of Samsung's more recent wearables will track sleep including the following: 

• Galaxy Watch 3
• Galaxy Watch Active 2
• Galaxy Watch Active
• Galaxy Watch
• Galaxy Fit
• Galaxy Fit e
• Gear Fit 2 Pro

Apple

Apple announced sleep tracking as a feature coming to watchOS 7. Currently Apple's smartwatch doesn't offer sleep tracking but it will when the watchOS 7 update arrives later this year with a dedicated Sleep app. 

Sleep tracking on the Apple Watch will use detection of micro-movements from the device's accelerometer to capture sleep stages, giving you a breakdown of your night's sleep and a chart presenting your weekly sleep trends in the Sleep app.

There will also be charge reminders if your Apple Watch doesn't have enough juice to get through the night and a Wind Down mode that works with your iPhone to help you wind down for bed, allowing you to snooze notifications, open meditation apps, turn on a music playlist or activate smart home presets.

WatchOS 7 and sleep tracking will be compatible with the following Apple Watch models when it arrives: 

• Apple Watch Series 3
• Apple Watch Series 4
• Apple Watch Series 5
• Rumoured Apple Watch Series 6

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