How does smartphone sleep tracking work?

Smartphone sleep tracking uses sensors inside your phone to watch how you move while you're asleep.

Your phone has sensors that are like tiny detectives. One of them is the accelerometer, which feels how you shift and roll during the night, just like how you feel when you're on a bumpy car ride. Another one is the gyroscope, which tells the phone if you’re turning over or sitting up.

Your phone keeps noting all these little movements and uses that information to make a story of your sleep, like how a bedtime tale is made from small events. If you don’t move much, it might say you had a deep sleep. If you moved around a lot, it might guess you were having trouble sleeping.

The phone can also use the light sensor to know when it's morning and you're waking up, just like how you know it’s time for breakfast when the sun comes in through your window.

Your phone doesn’t have to be on your body to do this; sometimes, it’s enough to just have it near you or on your bedside table.