Can you trust your watch's sleep tracking? Slide a night and see what it misses

Your watch gives you a sleep total and a chart of deep, light and REM, but it only senses movement and heart rate, not brain waves. Studies against sleep-lab measurements show wearables catch real sleep well but often miss the time you lie awake, and their stage guesses are shaky.

Slide your time in bed and time awake to see how much lying awake can inflate the total, then learn to use the numbers as trends, not verdicts.