It's supposed to see if you're moving. There was a time when I had particularly bad insomnia, laying in bed for hours unable to sleep, then I picked up my cell phone and it said I was in deep sleep. Actually I wasn't asleep, just not moving. Getting a good night's sleep is the foundation of being energized. For those of you who like to quantify your life, you might use apps like Sleep Cycle and Sleep Better on your iPhone or Sleep++ on your Apple Watch to track your sleep while you sleep at night. And both the former and the latter need to be tracked by opening the app and then pressing the Start button, and even the former needs to go through a strict positional placement if you have a partner so that it doesn't track the other person's sleep.

The need to count sleep really isn't a hard one, so this not-so-hard need that's still a pain in the ass to implement leaves one with no incentive to stick with it. --Hum

The new Sleep feature in iOS 11 does make it easy to keep track, but it's pretty one-dimensional. AutoSleep is one such app that automates sleep tracking, and all it needs is an Apple Watch. Interested in this app? Read Hum's AutoSleep, an attempt to fully automate sleep counting in the Apple ecosystem.