I found this Fitbit that gives some information on this:
"Sleep stages are traditionally measured in a lab using an electroencephalogram to detect brain activity along with other systems to monitor eye and muscle activity. While this method is the gold standard for measuring sleep stages (source), your device can estimate your sleep stages in a more comfortable, convenient way.
Fitbit estimates your sleep stages using a combination of your movement and heart-rate patterns. When you haven’t moved for about an hour, your tracker or watch assumes that you’re asleep. Additional data—such as the length of time your movements are indicative of sleep behavior (such as rolling over, etc.)—help confirm that you’re asleep. While you’re sleeping, your device tracks the beat-to-beat changes in your heart rate, known as heart rate variability (HRV), which fluctuate as you transition between light sleep, deep sleep, and REM sleep stages. When you sync your device in the morning, we use your movement and heart rate patterns to estimate your sleep cycles from the previous night."
Taken from: https://help.fitbit.com/articles/en_US/Help_article/2163.htm
Fitbit Product Experts Alumni are retired members of the Fitbit Product Expert Program. Learn more
Best Answer
