ATLANTA (AP) -- Your watch says you had three hours of deep sleep. Should you believe it. Millions of people rely on phone apps and wearable devices like rings, smartwatches and sensors to monitor how well they're sleeping, but these trackers don't necessarily measure sleep directly.

ATLANTA (AP) -- Your watch says you had three hours of deep sleep. Should you believe it. Millions of people rely on phone apps and wearable devices like rings, smartwatches and sensors to monitor how well they're sleeping, but these trackers don't necessarily measure sleep directly.