One third of the US population now owns some form of wearable to track their daily vitals according to a , whether that be the classic Apple Watch, the snazzy Oura Ring or the sporty Garmin Forerunner 265.  

As such, many people will be accumulating sleep data if they wear their devices overnight. While the patterns and information collated may vary slightly, you’ll often see the same trends: the ‘zones’ you slept in during the night, the length of your snooze and the overall quality of your rest – you may even get a sleep score out of 100. 

If you’re looking at this data and not knowing how to fully interpret it, then I’ve got good news. I had the chance to speak with scientist and Sleep Evangelist, . With a background in medicine, she’s worked on the award-winning programme (dedicated to improving a good night’s rest) and has been featured as a sleep expert on national TV and for some of the biggest companies in the world.  

She gave me a crash course on tracking sleep during the launch of the OnePlus Watch 2 Nordic Blue Edition in Helsinki, Finland. I also got a chance to ask her some of my most burning questions based on my years of experience of testing wearables for Tech Advisor.  

Here’s what you need to know about tracking sleep with your smartwatch or fitness tracker.  

Why is tracking your sleep with a smartwatch important?

Having a wearable that tracks your sleep may help you make decisions on what to do if you’re deprived and can give you an idea of what factors are making your night restful or not.   

According to Sophie, around 1 in 3 of the population are getting fewer than the recommended minimum of seven hours of sleep. Many adults tend to say they can ‘function’ on poor sleep and ‘adjust’ their schedule to fit with their lifestyle.  

This may be due to demanding careers such as medical professionals and athletes, to social butterflies who prefer to party hard, and of course, parents with babies and/or young children – no extra clarification needed there. 

However, sleep has a huge impact on our daily lives – especially when it comes to decision-making. Sophie experienced this herself when she went rock climbing in Dorset after just four hours of sleep.  

“As a result of this sleep deprivation, I made a number of truly stupid decisions that day. The person that I was climbing with, the route that I was doing, the time of day that I was climbing – culminating in a rather nasty fall. I had to be helicoptered off a cliff, and I spent a week in hospital having my ankle reconstructed… and I spent six months rehabilitating from the injury.  

“I recognised one important fact. It does not matter how much you know about sleep; it is what you do about it that really counts.” 

When many of us are regularly getting behind the wheel or jumping on the underground or even the simple task of crossing the road, reflexes and clear decision-making are vital, and a lack of sleep can have a huge impact on that.  

Sophie also says to consider your goals (be they physical, career or personal), and how more sleep could potentially help you reach them. Because after all, “sleep is the most potent form of recovery”.

What does sleep tracking data mean?

Most wearable data list the following ‘zones’ in sleep tracking: light sleep, deep sleep and REM (rapid eye movement). It will also report any times you were awake in the night.  

So, let’s break that down. In professional studies, there are four stages of sleep rather than three. However, most wearables combine stages 1 and 2 together, and call it light sleep. So, there’s no need to be alarmed if this makes up the bulk of your night, because that is very normal. As Sophie says, “Light sleep… is still valuable. You’re still refreshing your hippocampus, it’s all good stuff.” 

The hippocampus is our centre of working memory and we have one on either side of the brain. Sophie explains that they are relatively small, so after a certain amount of time we struggle to process new information. “What you need is sleep… to transfer memories from your hippocampus to your much larger cortex, which has loads more capacity.”  

Deep sleep is where your hormones are best balanced – where growth hormone and testosterone are produced. This zone is also useful for insulin sensitivity and reducing anxiety.  

The benefits of sleep continue in REM sleep, which typically occurs in the second part of the night. REM is particularly important for processing negative emotions, and problem solving. This is where dreaming occurs. If your sleep is disrupted, then you may see fewer periods of deep sleep and REM sleep and more periods of being awake.

Below you can see some sleep data captured from the OnePlus Watch 2.  

How reliable are wearables for sleep tracking?

This is a tricky one to answer, as most companies don’t publish the data that their metrics are based on. According to Sophie, that leading wearable brands such as Apple, Oura and Whoop are more than 90% accurate in detecting whether you’re asleep or awake.

But for sleep staging, we’re generally looking at 60-70% accuracy rating compared to the gold standard of monitoring with Polysomnography. Sophie says that “without measuring your brain waves, we can’t be completely confident that you’re getting it exactly right.” 

But that doesn’t mean the information isn’t useful – far from it.  

How to get the most from your smartwatch sleep data

Sophie stresses that wearing your smartwatch for just one night won’t cut it. “All of these devices are useful for exploring your own trends over time” and “what has an impact on your sleep patterns”.  

If you’re seeing disruptions, then you can try to identify what the root cause is. Some smartwatches can detect snoring and sleep apnea, which may indicate that you need to see a medical professional for help.  

You may also see hiccups if you’re having more than the recommended caffeine amount. Perhaps unbelievably, according to , you shouldn’t be having a pre-workout caffeine shot (typically >200mg) less than 13.2 hours before you sleep, as otherwise your deep sleep could be affected. The recommendation for coffee is to avoid it 8.8 hours before bed.

I very much shrunk into myself there, thinking about the millions of coffees and teas I consume in a day – often long past midday.  

Alcohol, stress, large meals before bed and exercise right before sleep can also mess with your rest. Therefore, if you want to improve, it’s worth slowly changing your habits over time, and seeing if there’s a correlation between the data and your new routine.

Sophie mentioned that most smartwatches are more likely to be generous with their sleep duration data. For example, I’ve noticed on multiple occasions that wearables don’t always catch when I wake up for a minute in the middle of the night… but that’s not necessarily a bad thing. 

“If your tracker tells you that you had a bad night’s sleep, it can have a negative impact on your performance the next day”. says Sophie. The power of psychology is effective, and if you’re then expecting that you’re going to be disrupted no matter what, then that’s likely to happen.  

If your sleep data is causing you anxiety, and as such making you worry about getting to sleep, then she has a simple solution. “Take it off. Have a break for a while, until you’re ready to worry a little bit less about the data”.

Sophie believes that the most important measure of how well you’re sleeping is how you feel during the day.  

How long should you use a smartwatch to track your sleep?

“At least a week” says Sophie, but truthfully, the longer the better.  

If you’re thinking about a lifestyle change, such as cutting down on caffeine or adding in more natural daylight to your schedule, then you should allow at least two weeks to see a tracked difference in your sleep – it won’t happen overnight if you’ll excuse the pun.

This could manifest in the duration of your whole sleep, or more specific zones such as the amount or proportion of deep sleep and REM. 

How else can tech be used to improve sleep?

That’s dependent on the person. Sound aids such as white noise, audio books or (my personal favourite) the pitter-patter of rain work for some, so you could use these through a pair of sleep headphones, or just from your phone/smart speaker. 

However, what works for one person may not work for another – we are all different. For example, Sophie mentioned that while many people can nod off to the sound of waves lapping in the ocean, others can become distressed as it provokes thoughts of drowning.

It may be a good idea to mitigate the amount you use your smartphone before bed, but Sophie emphasises that it’s maybe not for the reason you think. “These devices are designed to be addictive, the uncertainty of reward can create a hit of dopamine which is both alerting, and ensures that you stay stuck to the screen for longer than you planned.  

“The blue light effect is pretty neglible, because the intensity of the light from screens is actually very low. It’s a kind of myth about the blue light being alerting… a much bigger effect is the sleep displacement… because you keep scrolling.” 

The other items that Sophie recommends for sleep aren’t tech at all: eye masks and earplugs to block out light and noise. Again, test different things and see if there the results to back up your new habits.  

Providing you’re tracking your habits, and not being worried by the data, then you may finally be able to achieve the goal of more sleep… and who doesn’t want that? 

You can follow Sophie Bostock on tagram, and and check out her .