Certain devices say they can track how much and how well you sleep by measuring your bedtime tossing and turning. That includes fitness trackers, such as the Fitbit Surge, $250, and standalone devices such as the Beddit Sleep Monitor, $140, a thin sensor that you put directly on top of your mattress.

Both sleep tracker types sync to your smartphone or computer to create charts of how long it took you to fall asleep, how many minutes you were restless, and how long you slept.

Monitoring Your Sleep

But a sleep tracker that you wear on your wrist, such as the Fitbit, may overestimate sleep duration by as much as an hour, says Nathaniel Watson, M.D., president of the American Academy of Sleep Medicine, who helped review new sleep technologies in the December 2015 Journal of Clinical Sleep Medicine. That could be because the devices are attached to your arm, so if you’re awake but motionless, it’ll incorrectly record you as sleeping, he says.

The Beddit estimates sleep time using overall body movement as well as heart-rate and breathing patterns. Our tester, who used the Beddit and Fitbit Surge at home on different nights, found that even when he remained awake but motionless, the Beddit knew that he was awake; the Fitbit recorded him as sleeping at such times. But the Beddit app sounded its alarm early when it sensed that our tester was in a light sleep stage. (Beddit’s manufacturer claims that its optional “smart alarm” helps you wake up feeling more rested.)

Even if the devices aren’t completely accurate, they may alert some users to underlying health problems. For example, if they detect breathing disturbances, you may want to check into whether you suffer from sleep apnea, a condition—common in heavy snorers—that increases the risk of heart attack.

But for most people, the daily logs of time spent sleeping will simply make them more aware of their nighttime habits, Watson says. (Be aware that the apps may share your data with the manufacturer.)

Note that neither sleep tracker claims to be a medical device (intended for use in the diagnosis of a disease or condition) and as a result neither are regulated by the Food and Drug Administration. 

Editor's Note: This article also appeared in the February 2016 issue of Consumer Reports magazine.