[Tom Bottiglieri]

No matter what kind of ingenious seal/device you come up with to see if kids are in their rooms or not, they will find a way around it. Kids have a tendancy to want to break rules. Take it from me, I would know. Expecially when they know there is some kind of obstacle to get around to achieve their goal.

Also, even if you have something that makes it impossible for kids to get out of the door unnoticed, they will find a way to get out. (See: Drop Panel Ceilings; Balconies & Ropes)

But getting back to the question at hand, I think the best way to deal with this problem is to not try and force the kids to obey the rule. Do not try to play the part of "all powerful mentor" who can "get you in trouble". I mean, I know I would give much more respect to a mentor who treats me as an equal than one who is barking orders down my throat. And respect is the thing that would make me, as a student, obey certain rules. Also, as ngreen said, dont set an outrageous curfew; you are just asking for it to be broken.