Fitness bands and in-bed sensors cater to the data-driven who hope that the gear will ­reveal their sleep patterns, reports Consumer Reports.

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.