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Sleep Better

The Sleep Geek talks Sleep Trackers

Published 05 Feb 2025· 9 min read
A picture of James Wilson

Written by James Wilson

Sleep Expert

The Sleep Geek

As we come to the end of the first month of the year, where our renewed resolution to improve our health and wellbeing may be waning, many of us will have turned to a sleep tracker to give us a hand in being a better version of ourselves. But do sleep trackers help or hinder?

What is a sleep tracker?

Devices that track our sleep can take many forms, from a simple online diary, to a mattress topper that tracks your sleep. The most common form is the watch - using heart rate and movement to measure your sleep - movement based devices have been used in non-clinical settings like a poor sleepers home, using actigraphy or movement, for years. Popular “watch” type brands include, Whoop, Apple Watch, Fitbit, and Garmin.

You can also get rings that seemingly measure the same things, but using blood flow through your finger rather than the wrist - and these do seem more accurate than the wrist based trackers. As mentioned already some people use sleep diaries, whether digital or in a pen and paper form, and I have my own version of this which I call the kipometer (see below).

There are also phone based trackers, some that focus on sound like SnoreLab (which I am a massive fan of, for snorers), Sleep Score Labs and SleepCycle. The latter two use radio frequencies to track respiratory rate and movement (although it is not always clear, as these brands keep the algorithms close to their chest) and can be a bit temperamental in terms of getting a clear signal from the sleeper.

Finally we have topper based products, such as the Eight Sleep pod - which has tracking as one of the many claims it makes - or the topper from Withings, which claims to track sleep and screen for sleep apnea. 

The case for sleep trackers

Where trackers can be useful is as an engagement tool for someone who is struggling to understand their sleep and the impact it has on their health. For example, in football some players find using a tracker really useful when used like this, talking with me about their results, and using the kipometer alongside it - the lack of accuracy in the data is less important as we look at trends - and they are working with an experienced practitioner, who can give context to their data.

For good sleepers, trackers can be helpful as it reaffirms their good sleep and leaves them feeling positive about what they are doing.

Mattress Online’s CEO, Steve Adams, is a big fan of trackers - and his mindset around his tracker data is interesting. He likes to know how he has slept, whether good or bad, because he then feels like he can do something about it. If this sounds like you, then a tracker could be helpful to understanding your sleep.

The case against sleep trackers

In simple terms, most people I work with who have used a sleep tracker have found that it makes their sleep worse rather than better. Their expectations are often unrealistic due to the overblown claims made by the brands and their sleep expert advocates. 

Poor sleepers are given the impression that the tracker will give them an answer to their sleep issue, when in fact, they are a measurement tool that can give us an understanding of our sleep.

Mistrust on the data is driven by scores that don’t match the sleepers experience - along with a tendency for the messaging around results to be negative - for example when the sleeper feels they have scored quite well, but the tracker tells them people their age and gender generally perform better, this can leave many users disheartened.  The trackers encourage a desire to strive for perfect sleep, and often the user is left feeling like a failure

Does the research match what the sleepers I work with have to say?

The tracking brands are very secretive about their algorithms, usually based on movement, heart rate and heart rate variability - and how these data inputs are translated to work out when we fall asleep, when we wake up and how many times we wake,along with how long we spend in each of the four sleep stages.

The brands are often less eager to show that the product helps people sleep better, and are more focused on showing how accurate they are compared to Polysomnograph (PSG)  - which is said to be the gold standard used in clinical settings for the measurement of sleep and sleep stages.

It is worth bearing in mind that trackers are not usually used in a clinical setting, yet the research discussed below is mostly carried out in such sleep environments.

For example Oura recently conducted a study (Robbins et al 2024) of 35 healthy sleepers - comparing their 3rd generation ring device to the Apple Watch Series 8 and Fitbit Sense 2. The research showed that the Oura was the most accurate out of the three, although it is worth noting this research was carried out by Oura itself led by their Chief Science Officer, and didn’t include other popular brands like Whoop or Garmin.

This research was mirrored by a larger study this year by Svensson et al, that concluded;

“The Oura Ring Gen3 with OSSA 2.0 shows good agreement with PSG for global sleep measures and time spent in light and deep sleep (but note not REM sleep, contradicting the previous study).”

I would agree with the idea that the Oura is the most accurate of the consumer sleep trackers, so this research is not surprising - although I would argue, based on my use in the field,  it struggles to track REM sleep accurately - as the second study highlights.

Whoop carried out research in 2020 Miller et al, that found it was reasonably accurate when compared to PSG in knowing when you wake up and fall asleep - known as two stage sleep categorisation - but performed less well in four stage categorisation, so it struggles to know we are in deep sleep, or REM sleep - which again I see in my work that Whoop is noticeably poor at tracking these important sleep stages.

There is less research out there for the Apple Watch, who have focused on Actigraphy which is similar to the technology in wearables but configured to be used by clinicians, which it compared favourably to Caputo et al in 2024 - and as we saw above, it compared unfavourably to the Oura when both were compared to PSG.

Fitbit, Lim et al and Garmin Chinoy et al,have research with similar results to the Apple Watch.

When it comes to the sleep tracking apps on your phone that use radio frequencies - Sleep Cycle has no research to validate its sleep tracking (I find it useful for recording sounds, in snorers for example, but not tracking) and Sleep Score labs claims to be more accurate (Lee et al) than the likes of Fitbit for sleep and wake - but both in research and in use it struggles with getting a signal - so you end up with no data - and it lacks accuracy of the deep and REM sleep stages.

The most interesting thing about the research around trackers is the brands don't fund research to show that they help you sleep better. This is probably because, time and time again, research has shown the messaging from the brand - which sleepers often report as being overly negative and geared towards a narrative of failure - leads to worse sleep.

There are two interesting pieces of research on this. The first with insomniacs, Gaviloff et al - where poor sleepers slept with a sleep tracker using actigraphy (movement.) The poor sleepers then received fake sleep data the next day which either showed they had better, or worse, sleep than what they actually had..

Participants who were given the fake negative data performed worse on cognitive tasks, no matter how well they slept. Those receiving positive sleep feedback felt brilliant, less sleepy, more alert and in a better mood - the best versions of themselves.

A similar recent piece of research, which has not been published yet but was presented at SLEEP 2024 in Sevilla by Dr. Dale Rae, was carried out on healthy sleepers and had results that are more damning for the impact that trackers have. 

It was only a small study of 28 people but it showed in this case the fake negative data led to more objective sleep awakenings, they perceived their sleep quality was worse, they felt their sleep was less satisfying and felt more negative, emotionally.

In this study the data was only changed by 5%, and created such a significant change in performance and mood - and as the trackers own research shows - as they are more than 5% inaccurate compared to PSG, even at the level of accuracy they are running at they will be having a significant, potentially negative, impact on people’s sleep.

Should we use a sleep tracker?

I think it depends on what your relationship is going to be with the data - I think we have established that currently the data is not accurate enough, and if the data trends negatively then it can have a significant impact on your performance, and over time, your sleep.

But if you have a pragmatic relationship with data, and data reassures - whether good or bad - and you can use the data without it impacting your emotional wellbeing,  then a sleep tracker could be helpful - and particularly so if you measure things like heart rate, heart rate variability and temperature - all of which the trackers are generally better at tracking.

If you snore, or are trying to work out if a noise is waking you, then Sleep Cycle or Sleep Score Labs may help - as both are better at picking up sound than they are tracking your sleep.

For most people however, a tracker is more likely to make their sleep worse than it is to make it better.

Kipometer

When working with poor sleepers one on one I use what I call the “kipometer” - three key questions that allow you to work out if you are meeting your sleep need.

  1. How quickly did you fall asleep last night?
    • less than 5 mins
    • 5-30 mins
    • more than 30 mins
  2. How many times do you remember waking up?
    • I don't remember waking up at all
    • once or twice
    • 3+ times or less but for more than 30 minutes
  3. How do you feel at 10/11am in the morning?
    • rubbish
    • ok
    • alert and active

References:

  1. Accuracy of Three Commercial Wearable Devices for Sleep Tracking in Healthy Adults
  2. Validity and reliability of the Oura Ring Generation 3 (Gen3) with Oura sleep staging algorithm 2.0 (OSSA 2.0) when compared to multi-night ambulatory polysomnography: A validation study of 96 participants and 421,045 epochs
  3. A validation study of the WHOOP strap against polysomnography to assess sleep
  4. 0285 Measuring Sleep with the Apple Watch: A Comparison of a Machine Learning versus Traditional Algorithms to Actiwatch
  5. Correction: Lim et al. Patient-Reported Questionnaires to Identify Adverse Drug Reactions: A Systematic Review. Int. J. Environ. Res. Public Health 2021, 18, 11877
  6. Performance of seven consumer sleep-tracking devices compared with polysomnography
  7. Accuracy of 11 Wearable, Nearable, and Airable Consumer Sleep Trackers: Prospective Multicenter Validation Study
  8. Sham sleep feedback delivered via actigraphy biases daytime symptom reports in people with insomnia: Implications for insomnia disorder and wearable devices

About our Team

A picture of James Wilson

Written by James Wilson

Sleep Expert

The Sleep Geek

Through practical advice and guidance, James is here to help solve your sleep problems. Having faced the experience of sleep challenges, James is driven to help other people sleep better.

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