automatic sleep detection

Will new watch OS detect when I fall asleep? I have a varied sleep schedule and take naps as I can, will new watch OS be able to tell when I fall asleep regardless of what I set my sleep scheduled set at. I find it hard to always tell my apple watch when I am going to sleep. I got rid of my last apple watch and went with a fitbit simply for this feature. I would love to come back to apple if they finally had this capability.