Sleep monitors explained: Rest longer and feel better

Are you normal? We interpret your sleep data so you can rest easier
Sleep monitors explained
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Everyone's looking for a better night's shut-eye – and sleep trackers try and promise just that. But how can we use the data to get a better night's sleep?

What do all the graphs mean? How much deep sleep do you need? And should your chart really look like that?

Well, we've spoken to sleep experts and tried a range of trackers, from dedicated trackers such as the Withings Aura to the likes of the Fitbit Versa 2 and Garmin Vivosmart 4.

How does sleep tracking work?

Virtually every wearable device has the ability to map your shut-eye, but they don't all work the same. They all continuously monitor your movements during sleep – known in professional sleep circles as actigraphy – and assess sleep-wake cycles to see whether you're in deep or light sleep.

Can your sleep tracker help you to sleep better?

Every wearable device employs a slightly different sleep tracking method, but most don’t just track your sleep. Instead, they keep tabs on what your body is doing as you sleep to get the best guess about when you’re awake, in deep sleep and when you wake up during the night.

Tracking movement

The easiest way for a wearable device to tell when you’re sleeping and when you’re awake is by tracking movement. Many trackers and smartwatches contain sensors built to detect movement, like an accelerometer, which is how the tracker also measures the steps you take throughout the day.

These sensors can detect the subtle movements you make throughout the night to pinpoint when you go to sleep, the time you spend asleep, and when you wake up and walk to the toilet.

Movement sensors can also detect whether you’ve had a restless or restful night’s sleep, and can sometimes tell you how many times you woke up during the night too.

While all trackers take movement into account, for older devices it's the only data point on offer. That's why wearables that user heart rate have really pushed things on.

Tracking heart rate

Can your sleep tracker help you to sleep better?

Most of the newer, more expensive trackers and smartwatches tend to use other methods to track your sleep – the main one being a heart rate monitor, to measure your bpm as you rest.

Trackers then use this data to estimate either your beats per minute (BPM), your heart rate variability (HRV), as well as your resting heart rate (RHR) – or all three. This helps their algorithm to figure out not just when you’re likely sleeping or awake, but which sleep stages you’re in, whether that’s light, deep or REM.

This kind of sleep tracking is a big step up from movement because it’s not only more accurate – we’ve tried some devices that can get sleep and wake times wrong – but it shows you the different stages of your sleep.

We need all stages of sleep to feel properly rested, and sleep expert Clinical mental health therapist and sleep specialist Natalie Pennicotte-Collier told Wareable we need to cycle through light, deep and REM sleep – ideally five times in a night.

“Sleep Stages are a unique signature. It’s incorrect to say everyone should have 3 hours 46 minutes of deep sleep, for example. Just having the knowledge and sleep science doesn’t necessarily get you to change your habits,” Natalie said.

Data about sleep stages is useful because it could explain why you’re feeling more sluggish – maybe because you didn’t get enough deep sleep? Or it could hint at changes you could make to your routine, environment or anything else. For example, a lot of light sleep could mean you need to create a better sleeping environment in your room.

Tracking blood oxygen

The latest development is to track the amount of oxygen in the blood, which can alert to sleep disorders such as sleep apnea. It's estimated 22 million Americans suffer from sleep apnea, and many don't know they have it. Sleep apnea affects breathing, which can starve the body of oxygen and stop you getting the rest you need.

The Fitbit Versa and Fitbit Charge 3 are built with the tri-wavelength sensor on board, making relative SpO2 tracking/sleep apnea detection. It can also be found on the Garmin Vivosmart 4, Fenix and Vivoactive 4 smartwatches and the latest Withings ScanWatch.

But what is good sleep?

While most of us still think of a solid eight hours as being enough sleep, this doesn't take into account the number of times you wake up, or how much time is spent in each sleep cycle. We also vary, person to person, in how much sleep we need to feel recovered the next day.

A good night's sleep consists of around five or six sleep cycles. One cycle consists of the following:

Stage 1 – The drowsy, relaxed state between being awake and nodding off.

Stage 2 – A deeper sleep where your body temperature cools a little and you become disengaged from your surroundings.

Stages 3 and 4 – 'Deep sleep'. It's harder to wake up from deep sleep because this is when there is the lowest amount of activity in your body. It's also the part of sleep where your body rebuilds itself and restores energy, and hormones are released. This is the good stuff!

After deep sleep, we slip back into Stage 2 for a few minutes before entering 'dream sleep' – known as REM (rapid eye movement) sleep. Each cycle lasts around 1.5 hours and we need to experience all four stages in order to wake up rested.

What does a good night's sleep look like?

Sleep monitors explained: Rest longer and feel better

Sadly there's no such thing as a perfect sleep chart, but if you sleep like a baby and wake up refreshed your chart will almost certainly show a steady wave of peaks and troughs.

Generally speaking, a good night's sleep consists of cycles lasting for around 90 minutes. Notice that for every cycle the person goes into less deep sleep; this is typical for a normal sleep graph.

And while a few drinks can help you fall asleep faster, you can see from this graph that they also mean you'll probably have a lot less deep sleep, be more restless and wake up earlier than usual. Alcohol also tends to keep your heart rate higher.

But as Professor Colin Espie, world sleep expert from the University of Oxford and Chief Clinical Officer at Sleepio, explains:

"Each fitness monitor varies in the activities it monitors, the methods used to record them and the feedback given on the data collected. You may have to become your own detective to discover how the tracked data correlates with how you feel during the day and any factors that affect your sleep."

How much sleep is healthy?

Sleep monitors explained: Rest longer and feel better

Espie continued: "The number of hours' sleep you need is as individual as your shoe size. Don't assume you need the often-quoted seven-to-eight hours – in fact a shorter sleep may mean a better quality sleep."

The secret, according to the professor, is "discovering the sleep that you personally need, and then making that your sleep pattern."

To gauge just how much shut-eye you need, it is worth analysing how you feel on different amounts of sleep. Do you wake up drowsy after nine hours and struggle to drag yourself out of bed, or are you more productive with an earlier start to the day?

As a general rule however, newborn babies need roughly 12–18 hours, kids could do with 10–11 hours, teenagers (contrary to popular myth) only need around 8.5 hours while adults manage on 7–9 hours a day. So while there's some variation between individuals, nobody can function on four hours sleep a night and expect to remain fit and healthy forever.

How can we get more deep sleep?

Sleep monitor - Get more deep sleep

According to Professor Espie, "there are many small, practical steps you can take to make your day more sleep-friendly, from getting some exercise to cutting down on caffeine after lunch." But he recommends developing your own "personal wind-down routine".

Ideally this would consist of "an hour to an hour and a half before you go to bed when you don't do any work, avoid any 'stimulating' activity such as strenuous exercise, turn off any electronic devices and give yourself time to relax."

Easier said than done, especially if you like a night out and/or box set binges, but enjoying better sleep takes practice.

  • As unrealistic as it sounds, try and get to bed by 9:30pm at least twice a week. It will help pay off your sleep debt and make work more productive.
  • Avoid the lie-in at weekends as your internal body clock (circadian rhythm) doesn't stop for Saturdays. Force yourself out of bed and you'll sleep better during the week. Stanford sleep science expert Dr Zeitzer told us: "Changing your sleep patterns will indirectly, through differences in light exposure, change your circadian clock, which helps your brain to anticipate 'normal' or expected sleep timing. So, this would make falling asleep the next night difficult."
  • Call last orders at the bar at least three hours before bed time to give your body time to process the alcohol. If your blood is clear of alcohol, you'll sleep better.

How can you sleep more soundly?

Sleep monitors explained: Rest longer and feel better

"A reliable schedule is a critical part of being a healthy sleeper," suggests Professor Espie. "You should make the time to have a wind-down routine to help you relax before bed, and put your day to rest. Aim to stop your work/activity at least 60-90 minutes before bed, and keep your bedroom dark to help signal the body that it's time for bed."

"Give your mind something to focus on; one technique that's proven to work is using imagery. Imagine a scene that is calming and relaxing like walking through a favourite park or sailing in a gentle breeze – something that is engaging rather than exciting to the brain."

If you're unsure what to do with your sleep data, apps such as Sleepio sync with data from devices from trackers to help build a weekly plan, using CBT (Cognitive Behavioral Therapy) techniques, to help train your mind and body into sleeping better.

You should also be wary of external factors that can impact your sleep. During our sleep diary, we discovered this was a key issue. Light, sound, and even dust are all things that can interfere with rest. If you think your sleep is suffering, you can try to ascertain any external factors that may be causing it. Devices like the Withings Aura keep a lookout for these things.

However, as we found in our sleep diary, overanalysing sleep can end up having the reverse affect. Getting good quality sleep is important, but over-obsessing leads to stress that might only stop you sleeping well. For that reason, it might be worth finding a device that can track your sleep with as little required input each night from you. No one tracker out there is perfect, so you have to weigh up what's most useful to you.

How can you fall asleep faster?

Sleep monitors explained: Rest longer and feel better

Worrying about not sleeping, the to-do list waiting at work or the state of your bank balance will keep even the heaviest of sleepers awake at night, but how can you get to sleep quicker? Follow these tips for a better night's kip:

  • Bedtime routines aren't just for toddlers: a relaxing bath or listening to soft music can help you prepare for sleep.
  • Turn down the thermostat as it is easier to sleep soundly in a cooler room.
  • The more you exercise, the more likely you are to improve your sleeping patterns.
  • Eat pumpkin seeds – they contain high amounts of zinc, which can help the brain convert tryptophan into serotonin which helps you sleep easier.
  • Don't drink caffeine after lunch and go easy on the alcohol.
  • Turn off your tablets, as light from gadgets can inhibit and delay the production of melatonin, making it more difficult to get to sleep.
  • Some of the bedside devices use a mix of light and sound to help soothe you into sleep. If you struggle drifting off, it might be worth giving them a try.
  • Avoid spending time in bed when you're not sleeping, as you need to create a positive association with being in bed and being asleep.
  • Learn to listen to your body – if you're feeling tired in the evening, it's probably time for bed. As Dr Zeitzer told us, "When your brain gets tired but you 'fight' the tiredness (ie, try to stay awake), it compensates, we think, by overdriving wake-promoting systems. As the effect of overdriving these wake-promoting systems wane, the tiredness comes back and you either go to sleep or get another jolt of wakefulness. This is most obviously seen in younger children, though it still happens in adults, it's just less obvious."