Tried doing the same experiment, sleeping with no alarm clock. I think it kinda make me more aware to wake up. I think I woke up twice in the night. Probably a shift in the dreams perhaps, I know I was awake because I knew I shifted position in my sleep. So far on my second day of the "no alarm" it seems I normally sleep 7 hours before I naturally wake up. However this does include the factor that drifted out of sleep during the night, so perhaps this is factor that needs to be put into consideration. Another thing I did is, to sleep when my body asked me too. Instead of using television, Internet, video games or even work to keep me up. With this set up, it kinda works with having reduced or no social life at all, because I do return late after the lab, and I do spend time with the family. I feel married in a sense already. At least time worth spending with the family is worth more than the time spent with people not related to you by responsibility, law or marriage.