Why Do Smartphones Know Exactly When to Wake You Up?

Smartphones can tell when you're asleep because they use sensors like your phone's accelerometer. These little sensors work like a mini-motion detector, they feel the tiny movements of your body as you sleep or wake up, just like how a toy car detects motion on a road. If your phone notices that you’ve been still for a while, it thinks you're sleeping and knows when to wake you up gently with a soft vibration.