Are sleep trackers accurate?

Sleep trackers claim to measure the total amount of sleep we have each night; the time spent in different stages of sleep (light, deep and REM); our sleep schedule and provide an overall sleep score.

Sleep trackers rely largely on movement to detect if we are asleep. Most trackers overestimate the duration of sleep because if you lie in bed, it thinks you are asleep. Newer watches have additional technology to measure heart rate, breathing and heart rate variability to estimate sleep stages. A study in 2021 examined 7 sleep trackers and found the devices were fairly accurate at detecting whether we are awake or asleep but not accurate at detecting the different stages of sleep. Another study in 2023 looking at 11 sleep trackers had similar findings – the accuracy of sleep stages falls well short of data from sleep studies conducted in a sleep lab.

So, are sleep trackers helpful or harmful?

For most people, sleep trackers provide some interesting sleep data with minimal effort on our part. Trackers certainly have the capacity to be very helpful if they lead to consistent behavioural change that means we sleep longer and wake up feeling rested and refreshed.

The downside to sleep trackers is that for some people they create a new anxiety about sleep that was not previously there. For example, you wake up in the morning feeling pretty good, reach for your phone and check your sleep data from last night. Your app tells you that your sleep quality was poor and you did not have enough REM sleep. You are now worried about being tired at work. You worry at night time that you might have another poor night’s sleep and so it takes you longer than usual to drift off. And so, begins the worry cycle about sleep. Checking data too often and feeling anxious about sleep is the potentially harmful impact of sleep trackers. If you notice this happening, it is time to take your watch off when you go to bed and rely on how you feel in the morning to know whether you got a good night’s sleep.