SleepPayAnything that measures your heart at night.
Rings, straps, watches and mattress sensors all work. Connections are read-only and go through each maker's own authorisation screen.
Not on the list?
If it writes sleep and heart rate to Apple Health or Health Connect, it works through that bridge today: Coros, Amazfit, Polar, Suunto and most others.
Which scores best?
None. Scores compare you to your own 30-day baseline on the same device, so a ring and a watch reach the same number for the same night.