Quick Links
Sleep has joined steps as one of the activities we expect smartwatches and trackers to keep tabs on. This is especially true of Fitbit’s offerings, which advertise features like “sleep score” and “smart wake.” But how does Fitbit’s sleep tracking actually work, and is it reliable?
How Fitbit’s Sleep Tracking Works
Fitbit’s wearables, including smartwatches like the Google Pixel Watch that use Fitbit technology, detect the necessary information to track sleep using a multitude of sensors.According to Fitbit, these include a multi-path optical heart rate tracker, multipurpose electrical sensors (ECG and EDA), gyroscope, altimeter, 3-axis accelerometer, temperature sensor, ambient light sensor, and GPS receiver (with GLONASS).
Together, these sensors can track movement and direction, changes in height, proximity to your wrist, blood oxygen levels (large swings can be a sign of sleep apnea), heartbeats per minute, body temperature, and the resistance of your skin to small amounts of electricity (a method known as bioimpedance, used to estimate body and muscle fat). Quite frankly, Fitbit devices pack a lot of techto make sleep tracking work.
Early Fitbit models determined whether a wearer was asleep by measuring movement. Newer devices also track your heart rate to provide deeper insights into the stages of your sleep, such as light, deep, and REM sleep (when we dream). All newer Fitbits use this information to generate a “Sleep Score”—as long as you have a Fitbit Premium subscription.
How to View Your Fitbit Sleep Score
Fitbit’s Sleep Score ranges from 1 to 100 based on the length and quality of your sleep. The sleep score appears as soon as you open the Fitbit app on your phone. You can tap on the sleep score to view more details, and Fitbit provides you with layers of information. There are ample ways touse Fitbit sleep profiles to help you sleep better.
In addition to the amount of time you spend asleep, a horizontal graph displays the nuances of your rest. Red parts are times when you’re awake. Light blue indicates REM sleep, a slightly darker blue indicates light sleep, and the darkest blue indicates deep sleep. Fitbit doesn’t always use the same colors across devices, so don’t be confused if your Google Pixel Watch utilizes shades of purple instead of blue.
50% of the score is determined by the length of your sleep, 25% by how much time you spend in deep or REM sleep, and 25% by how peaceful or agitated you were during your slumber.
What Impacts Your Fitbit’s Accuracy
As something you wear on your wrist, your Fitbit needs a snug fit to provide reliable results. You need to wear the device consistently from one night to the next—for at least 14 days—to get valuable feedback. You must also ensure your device is charged enough to make it through the night.
Some factors are outside of your control.Research by the Sleep Research Societyfound that the photoplethysmographic green light in the back of many fitness trackers has a more difficult time measuring the heart rates of people with darker skin tones.
Have Third Parties Verified Fitbit’s Accuracy?
Wearables like the ones offered by Fitbit have become popular among sleep researchers due to their ease of use and low cost.
A 2019 study in theJournal of Medical Internet Researchanalyzed several previous Fitbit-related articles to see what researchers had to say about how viable the products were for academic research. The results show that Fitbit devices provide helpful trend data, but the results aren’t accurate enough to substitute for polysomnography.
This isn’t a slight against Fitbit per se. Polysomnography takes in more data by monitoring your brain waves, breathing, and eye movements in addition to the type of information that a Fitbit can gather. Even if youopt for a smart mattress over a sleep tracker, you won’t get that much data.
How Fitbit Compares to Other Sleep Trackers
It’s difficult to compare the results of fitness wearables directly, even if you happen to get your hands on more than one device. Sure, you’re able to wear multiple devices at once, but you can only have one in the optimal position on your wrist at any given time. That’s also assuming you aren’tcomparing the accuracy of different sleep trackers.
ZDNetperformed this type of direct comparison of the Fitbit Inspire 2 and the Apple Watch Series 7, finding slight variations in the results. This sort of anecdotal observation doesn’t show whether one is more accurate than the other; only that there is a noticeable difference.
An earlier 2020 study published by theNational Library of Medicineconfirms these results, noting that various consumer sleep trackers display inconsistent information regarding sleep stages and concluding that none could replace a sleep analysis in a lab. Another 2020 study in the journal Nature and Science of Sleep,published by Dovepress, reported similar observations:
Generally speaking, commercial sleep technologies displayed lower error and bias values when quantifying sleep/wake states as compared to sleep staging durations. Still, these findings revealed that there is a remarkably high degree of variability in the accuracy of commercial sleep technologies…
Different outlets will give you mixed recommendations on which fitness tracker is the best.WareableandVerywell Healthlist Fitbit devices as the best wearable options for 2023.CNNalso lists Fitbit, among others, as one of the best sleep trackers of 2024. However,Sleep FoundationandWirecutterdon’t list Fitbit at all.
The primary difference between all of them has more to do with comfort and features than the reliability of results. In short, Fitbit’s sleep accuracy is no better or worse than much of the competition’s offerings.
