Didn't we have a similar question awhile ago?
Skin temp: basically impossible
Eyes: extremely impractical. Not only would it be very advanced for a machine vision application to determine this, but you'd also need cameras from different directions. I could still always find an angle not covered by a camera.
Motion: Well, you can detect when somebody walks by, but that's not really the question. You can't point a PIR motion detector at the bed either. Awake people sometimes don't move. Sleeping people turn over in bed which can set off a PIR.
Respiration, heartbeat: not all that consistent, and you need sensors hooked up to the person.
Basically "asleep" is a pretty tough determination. It's only really possible with brainwave measurements. I'm not sure if wiring up a person's head is what you have in mind though.