Fitbits have quickly evolved in recent years from the small silicone devices that only measured basic physical activity when you were running or walking. Now they are capable of everything from receiving calls, paying for your shopping, tracking your location with GPS, playing music, and even tracking your sleep patterns.
The nifty devices come in band trackers and smartwatches that are dedicated to recording various types of biometric information such as your heart rate and blood oxygen level, all in an attempt to help you better understand how your body is performing. Along with their other functions, sleep monitoring on Fitbit watches has also evolved, and most models now collect all kinds of data that help you understand what sleep patterns look like and whether you’re getting the sleep you need–without the need to download a third-party sleep tracking app.
How Does a Fitbit Monitor Sleep?
When you go to a sleep clinic for professional sleep monitoring, you’re hooked up to a range of machines that measure features of sleep like how relaxed your muscles are, whether you are experiencing rapid eye movement, and even your brainwave activity.
While it’s not fair to expect that level of sleep monitoring from a compact smartwatch or tracker, the Fitbits of today have been tried and tested with excellent results, and are able to give you data-driven insight into your sleeping behavior.
A Fitbit will use your heart rate variability to detect the change in your sleeping levels, i.e. from light sleep to the deepest kind of sleep, and even REM. The motion of your body is detected by the internal accelerometer, which can tell when you are immobile and sleeping as opposed to sitting quietly reading a book. Some Fitbits can even monitor your skin temperature to give feedback on whether you need a lighter duvet or if your high temperature is related to nighttime restlessness.
Fitbit has even partnered with the National Sleep Foundation and worked with sleep experts to refine their sleep tracking algorithm and features. The Fitbit can detect light sleeping periods, which have benefits for the body and mind (this is the reason “power naps” can be so refreshing), as well as deep sleeping periods, which are also necessary and which assist with body repairs made by the immune system and have links to both learning and memory tasks.
REM sleep occurs after this, and the Fitbit notices the rise in heart rate as you begin to dream. This sleep is essential for this body as well as for mood regulation during the daytime.
A Fitbit takes these various stages and presents them to you in an easy, accessible way through the use of charts and graphs so you can make correlations between your behavior, mood, and alertness during the day and how you slept.
How Accurate Is a Fitbit at Monitoring Sleep?
Fitbits are quite effective at noticing when you’ve fallen asleep compared to some other devices, and this alone makes them some of the best sleep trackers available. However, the device’s determination of the length of the stages you’ve slept through–light, deep and REM–will not always be fully accurate.
Studies conducted on Fitbits regarding polysomnography (what your body does when it’s sleeping) showed that models such as the Charge 2 can accurately measure the amount of time you’ve slept and the “efficiency” of your sleep. However, the best indicator will be your subjective experience of your mood and energy levels the next day, since the Fitbit may not always give an accurate reading regarding how long you’ve been in, say, REM sleep.
For example, if your Fitbit says you’ve not had much deep sleep and you are having trouble concentrating, this would be an indication that the two events are correlated. Or if you’ve woken up feeling really refreshed and full of energy, and you see you’ve had lots of sleep in the REM stage, then you can put the data together yourself and see if that trend occurs again.
One particular study showed that Fitbits tend to overestimate how long you stay in one stage of sleep and underestimate the biometric feedback which indicates you are moving into another stage, thereby skewing results.
What Functions of Sleep Monitoring Does a Fitbit Have?
Below is a list of the sleep-related features offered by the latest Fitbit devices.
Sleep tracking: By simply wearing the Fitbit, your waking and sleeping patterns are automatically discerned by the algorithm, which takes into account your movement and your heart rate.
Silent alarms: Being woken up suddenly by a loud noise jolts you out of deep sleep and can have a negative impact on your day. Quiet alarms use gentle vibrations on your wrist that become progressively stronger until you wake.
Smart wake: This feature allows you to set a specific sleep stage that you want to be woken up during; for example, after you’ve moved into light sleep for half an hour after being in deep sleep.
Sleep stages: As we mentioned previously, Fitbits can let you know how long you’ve spent in both light and deep sleep, as well as the time of REM you had. This data can give a good general idea of your sleeping patterns, though it may not always accurately reflect the exact amount of time spent in each stage.
Sleep score: Using multiple types of data, from slight restless movements to high heart rates, the algorithm gives you a single score every morning that reflects the quality of your sleep. This makes it easy to see patterns in your sleep without spending too much time digging through data.
Sleep schedule: Stay consistent with your sleeping patterns to give your biological clock some stability. The Fitbit lets you set what time you want to go to sleep, and when you need waking up.
Bedtime reminders: Sometimes we can get carried away with a book or a film and need that nudge telling us it’s really time to head to bed and get some sleep. Reminders can help your body develop healthy routines.
Sleep insights: Get an overview of your sleeping behavior, from your heart and breathing rates to how much you moved around and how much time you spent dreaming in REM.
Snore detection: Available on a Premium plan, you can set your Fitbit to take note of the decibel level of your snoring and how long you are snoring for.
Which Fitbits Can Monitor Sleep?
There are many models of Fitbit which can monitor sleep, but some of the best ones are the Fitbit Charge 2, the Fitbit Versa 3, and the Fitbit Sense. Some Fitbits such as the Fitbit Surge and Fitbit Charge HR may have heart rate monitors, but this alone doesn’t allow them to record accurate sleep levels, only sleeping and waking times, so you’ll want to keep that in mind if you’re seeking out a Fitbit primarily for its sleep tracking features.