You spend around a third of your life asleep, with the amount and quality of sleep having a huge impact on the rest of your life.
So it’s natural to be curious about how long you really sleep for, and whether you’re getting enough good quality sleep without any sleep disorders to address.
Until just a few years ago, your options for assessing your sleep were somewhat limited: you could keep a sleep diary if you had the dedication; ask your partner about your sleep, or record yourself sleeping (an unlikely activity!)
The only way to accurately assess your sleep would be to spend a night or two in a specialist sleep clinic. But now there’s another option to improve your accuracy of self-assessment: the personal sleep tracker.
A question of accuracy
How do consumer sleep trackers work though? How do they compare to the equipment and expertise in a sleep lab? And can you actually rely on the information they provide?
These are important questions to consider, especially if you’re thinking of spending a fair bit of money on one.
Hopefully, this article will give you a better understanding of what you can expect from your sleep tracker.
Common sleep tracking features
In their most basic form, sleep trackers track whether you’re asleep, and how much time you spend asleep. Typically, however, sleep trackers often measure several aspects of your sleep:
The amount of time you spend asleep. The sleep tracker will analyze whether you’re asleep or awake, and chart the total amount of time you spend asleep.
The quality of your sleep. Sleep trackers will analyze any movement during your sleep, to assess whether your sleep is restful or restless.
How much time you spend in each stage of sleep. Some sleep trackers claim to track how much time you spend in each stage of sleep. Using this information, they’ll schedule your alarm to go off at a time when you’re likely to be in light sleep, making it easier for you to wake up.
The quality of your sleep environment. Sleep trackers may analyze other factors that can impact the quality of your sleep, such as the light or temperature in your bedroom.
Sleep-related health metrics. Much of what you do during the day can actually impact your sleep, such as your diet and exercise. Throughout the day, some sleep trackers may track your physical fitness, heart rate, food consumption, and stress levels to analyze how your daily life may be affecting your sleep.
How do sleep trackers know when you’re asleep?
The main way sleep trackers know when you’re asleep is through your body movement. While we switch positions during sleep and may twitch some during our dreams, we’re generally a whole lot more still when we’re asleep than when we’re awake. This makes body movement a useful indicator for measuring your sleep vs. awake status and your overall time asleep.
Depending on the type of sleep tracker you have, it will measure your body movement through either actigraphy or accelerometry. Most wearable sleep trackers leverage actigraphy, where an actigraph sensor is worn around your wrist. Many smartphone sleep tracking apps, on the other hand, rely on the phone’s accelerometer to measure your body movement and assess whether you’re asleep or awake.
In addition to your body movement, sleep trackers may also measure the following personal and environmental factors to determine when you’re asleep or awake:
Your heart rate
Sleep trackers with a heart rate tracking feature can measure your variations in heart rate (or lack thereof) to assess when you’re asleep or awake and make a more informed assessment of when you’re in REM sleep.
When you fall asleep, your heart rate slows down and blood pressure both lower. Your heart rate stays fairly steady through the duration of your sleep—with the exception of REM sleep. In REM sleep, as when you are awake, you can experience an increase in heart rate and overall more variations in your heart rate.
Wearable sleep trackers use personal heart rate monitor (HRM) technology to measure your heart rate, while mattress sleep trackers use ballistocardiography (BCG). Ballistocardiography is an alternative way of measuring your heart rate by observing the repetitive motions of your body, as opposed to being attached to your skin through a HRM sensor. The mattress strip in mattress sleep trackers may include a BCG sensor to measure how your body movement affects the movement of the strip.
Are Sleep Trackers Worth It?
If you’re the kind of person who benefits from knowing you’re being monitored to reach your goals (or if you’re simply interested in seeing the metrics), a sleep tracker may be worth it. For the most part, these devices reliably know when you’re asleep and how much time you spend asleep.
The recommended amount of sleep is 7 to 7.5 hours for adults per night. However, studies show people often overestimate how much sleep they’re getting. This is one area where a sleep tracker comes in handy, as you can use it to find out if you’re getting enough sleep per night. Also, if your sleep tracker includes a mic, you can use yours to find out if you’re snoring at night.
On the whole, sleep trackers can help you do a better job monitoring when you go to sleep when you wake up, and how much sleep you get overall. However, you may want to take their graphs about your various sleep stages with a grain of salt.
Also, if you’re the kind of person who gets stressed out from monitoring your health so closely, a sleep tracker may do you more harm than good. Some people can even become obsessed with monitoring their sleep, a condition known as orthorexia.