I have a cheap smartwatch (amazfit bip) that tracks sleep and I have found it to be very accurate for me. I assume it tracks when I fall asleep based on heart rate and movement?
Anyways it plays nicely with my android phone and only cost about $50 and honestly I’m pretty happy with it! I was pretty skeptical at first but it’s really handy as a fitness tracker too and I feel like it encourages me to stand up and exercise more.
I also have a somewhat erratic sleep schedule and it’s nice to know when I’m starting to get into a sleep deficit and need to get caught up.