Getting an Apple Watch really hit home how bad alcohol is for sleep. Anything more than a drink four hours before sleep absolutely destroys my deep sleep. I go from ~3.5 hours of deep sleep to 1 or less. My resting heart rate is also 10 or 15 bpm higher while I sleep than when I don’t drink

Is the watch really accurate to measure deep sleep?

Are there any other watches/devices which measure deep sleep?

Not sure how accurate it is but the fact that it's so reproducibly different does make me trust it a little bit. Also jives with how tired I am the days after I drink. The resting heart rate seems to be quite accurate, I've compared it to manually checking my pulse. During exercise it tends to be slightly less accurate because of the sweat and movement.

There is a Xiaomi product that supposedly can do this: https://www.mi.com/en/miband/