Sleep trackers have been getting more and more popular over the last several years. At this point, there are sleep tracking apps, wristbands, mattress pads, and even rings. However, a lot of people take their sleep tracker’s data with a grain of salt. After all, how accurate can something be if it’s not measuring your brain waves to know when you’re actually asleep and awake.
Are you wondering if there’s any benefit to tracking your sleep? Here’s everything you need to know so you can make an informed decision.
Why Should You Track Your Sleep?
People track their sleep for all sorts of different reasons. Those with sleep disorders often use the data to get an objective point of view on how they are sleeping, so they don’t have to go with their own feelings and perceptions alone. Sometimes, they feel like they are sleeping better or worse than they actually are, and a sleep tracker can give more objective data.
Other people do it for just that: the data. Some people like to assign numbers to everything, so they enjoy knowing how much sleep they got, how much of it was deep sleep or REM sleep, etc. They may or may not find it actually helpful, but they enjoy looking at the information.
Finally, some people use sleep trackers to keep them accountable for getting enough rest. If you’re someone who likes to say up late or who ends up prioritizing other things over your sleep, then a sleep tracker can help keep you on track. It will give you useful data about how much you sleep, so you can make sure that you’re getting enough sleep and not making excuses for your lack of rest.
How Do Professionals Track Sleep?
There are several ways to track sleep. If you go into a lab for a research study and sleep there, they will use polysomnography (PSG) to measure your sleep. This involves attaching electrodes to your scalp so they can use EEG to measure your brain waves. They may also measure other things, like heart rate and body temperature, to make doubly sure that you are asleep when the EEG indicates.
Since most of us don’t want to sleep in a lab regularly (and don’t have that option), the best choice is actigraphy. Actigraphy is a measurement of how much you are moving, or how active you are. Actigraph devices are usually worn on the wrist, like some of the more common sleep tracking devices you might be aware of. While these don’t have the same level of accuracy as PSG, they are used in formal studies that measure sleep patterns and habits.
Monitoring the heart rate and/or skin temperature in addition to actigraphy makes the results more accurate. Some of the wrist-worn devices have been designed to add one or both of these features, as well. Since your heart rate accelerates and decelerates depending on what sleep stage you’re in, and your skin temperature changes, too, these devices can help ensure that the data researchers get is accurate. It also allows them some sense of which sleep stage a person is in, which actigraphy alone may not be able to do.
How Do Sleep Trackers Work?
Most of the popular sleep trackers on the market today are worn on the wrist, and many double as a step-counter, exercise tracker, heart rate monitor, and more. There are also apps that claim to track sleep, as well as pads that you can put under your mattress to track your rest. These usually connect to an app or another device so it’s easy to get your results.
The majority of these sleep trackers rely on actigraphy, though some also combine heart rate technology and/or skin temperature monitoring to add to their accuracy. Most of the ones that include the heart rate or skin temperature are worn on the wrist, where it’s relatively easy to pick up your heartbeat and where they have direct contact with your skin. In general, if your sleep tracker has heart rate monitoring technology as part of its other capabilities (usually exercise monitoring), then it can also use that data to determine whether you’re asleep and what sleep state you’re in.
What Sleep Trackers are Available?
The Fitbit family of exercise trackers are among the most common wrist-worn sleep trackers. Some of these devices are limited to actigraphy only, but many of them now offer heart rate monitoring technology, too. Some of them offer information on your sleep stages, while others will only tell you when you were awake and when you were asleep.
A few of these devices have been shown to be about as accurate as EEG monitoring. While the main study on these devices was conducted by the company itself, and so should be interpreted with at least a bit of skepticism, it was verified by independent researchers, which adds credibility.
Among the apps available to monitor sleep, two of the most popular are Sleep Coacher and Sleep Cycle. Sleep Coacher asks you some questions about your rest, then makes recommendations for you to follow. It has you follow them for several days, then ignore them for a few, to see if you notice a difference in your sleep. It also requires you to keep your phone on your bed at night, so it can monitor your sleep, via actigraphy and noise monitoring, to give you an idea of what helps.
Sleep Cycle doesn’t give you recommendations for your sleep, but it does monitor your sleep and set off your alarm at a time that is good for you, based on what sleep cycle you’re in. It takes into account any movements you make, as well as any sounds it picks up from your or in your bedroom. You may have to experiment with where to put your phone to get this app to work at its best.
When it comes to sleep trackers that go on your mattress, Eight is popular. It is actually a mattress pad, and, in addition to monitoring sleep, it will also warm your bed and connect to various wifi devices that you might have. It also provides an alarm, similar to that in Sleep Cycle, that wakes you at a time that’s good for your sleep. There’s not much data on how accurate it is, but reviews indicate that people seem to think it helps them get a better night’s rest.
How Accurate are Sleep Trackers?
Since you probably won’t be hooking yourself up to a PSG device every night, we’ll focus on the accuracy of actigraph devices. However, most of the studies out there have been done on devices built specifically for actigraphy, and not on the popular wrist-worn devices that also track things like exercise, steps, etc. That said, there has been at least one study that included a Fitbit among the actigraph devices tested
Actigraphy alone seems to be generally accurate when it comes to healthy adults who have relatively normal sleep patterns. If, however, you have a sleep disorder, the devices become less and less accurate the more disturbed the sleep becomes. This is because people with sleep disorders tend to move around more in their sleep, which the tracker can interpret as being awake or frequent waking.
These trackers cannot be used to determine which sleep stage you are in. Since they rely on movement alone to determine sleep stages, the best they can offer is a very limited generalization. This does change if the tracker takes heart rate into account when determining sleep stages, since your heart rate changes depending on the stage you are in. However, even these trackers will only give you a general idea of how long you spend in each stage, since they aren’t monitoring your brain waves.
How Do I Choose a Sleep Tracker?
Researchers warn that even the most accurate trackers will probably not get your sleep duration perfect. Most of them either overestimate or underestimate how much sleep you’re getting. They may assume that you are asleep when you are lying still in your bed, wide awake, or they may assume that you are waking in the night when, really, you are just restless in your sleep.
Given this data, as long as you are using your sleep tracker to give you a general idea of how much and how well you are sleeping, it is probably a worthy device. After all, scientists use them all the time and rely on the data they offer. If, however, you want to know exactly how long you are sleeping and how long you are spending in each stage, they aren’t going to help you a lot. The technology just isn’t there, yet, to give you that level of accuracy on a device you can wear every day.
If you decide to get a sleep tracker, it can help you reach your sleep goals. It might help you do your best to note what time you fall asleep, what time you wake, and how long you are awake at night. Then, compare the data to your sleep tracker. Doing this for a few nights can help you determine how accurate your tracker is. Then, you know how much you have to generalize the results you get from it.
In the end, sleep trackers are valuable, especially if you aren’t sure how much sleep you’re getting or you want to hold yourself accountable to sleep more. Even though you can’t completely trust the results, they can help you remember to get more sleep and give you feedback about whether you are getting the sleep you think you’re getting. If these uses appeal to you and fit your needs, then it’s time to get your very own sleep tracker.