Put the phone on the bed beside you. It reads breathing and body movement from the accelerometer, and estimates sleep phase from them.
Ready. Press Start, then put the phone face-down on the mattress, near your chest.
0:00
Elapsed
—
Breaths / min
—
Movement
—
Latest phase
—
Sensor Hz
Sleep phases
AwakeREMLightDeepNo signal
The night
How to get a good recording
Where to put it: face-down on the mattress, roughly level with your chest, within arm's reach. On the pillow works too; on a bedside table does not — it has to be on the same surface as you.
Keep it awake: the accelerometer stops when the browser is backgrounded or the screen locks. Leave this page in the foreground and plugged in; the page asks to hold a screen wake lock where the browser supports it.
iPhone in Safari: motion access needs an HTTPS page (or localhost) and a permission tap — that is what the Start button asks for. Gaps show up on the chart as "no signal" rather than being hidden.
Two people in the bed: the phone reads whoever it is closest to, but a partner's movement lands on it too, and will be scored as yours.
What it can't do: lying still and awake looks like light sleep to any movement-based tracker, this one included. Treat the phases as an estimate of the shape of a night, not a measurement.