There are mobile apps or fitness watches/bands that apparently can tell your sleep state based on your movement etc. I don't know how accurate they are because

There are mobile apps or fitness watches/bands that apparently can tell your sleep state based on your movement etc. I don't know how accurate they are because my phone is cheap with cheap sensors. You tell these apps what time you want to wake up at the latest, and they will ring the alarm before that time when you are not in deep sleep.