It depends on the device. I used to use the Microsoft Band 2, and it seemed pretty good to me - at least it helped to validate what I believed to be my sleep p

It depends on the device. I used to use the Microsoft Band 2, and it seemed pretty good to me - at least it helped to validate what I believed to be my sleep patterns. In contrast, I now use a Garmin Fenix 3, and it's completely and utterly worthless for sleep tracking - it routinely decides I'm sleeping when I'm in bed even if I'm on my phone or change the display on the watch, and it rarely picks up the times I wake up during the night. --It's too bad, because for activity tracking throughout the day it's actually really good. But doctors don't seem to trust the consumer devices (probably with good reason). When I had an actigraphy, they used a special device made by Phillips, and used the results to verify that the sleep study results weren't a one-off night.