what about a safety alarm for the inside?

Many parents with AD kids have to use door alarms. They need to know that little Johnny is staying put for the night and not prowling for food or worse, people to hurt. At my house, I need an interior alarm. All joking aside...I don't like how often DD seems to be hurting herself lately. It started with the teeth, moved on to purposefully bruising herself (baseball to shin creates large purplish black bruise) and other little things are showing up. I don't seem to be able to catch her 'in the act' anymore and she is really having to try to sneak it - because she's in line of sight a good majority of the time. There are just times when I send her to bed and I worry. Tonight is one of them. I'm upstairs at the computer so that I can go in and check on her every 30 minutes or so, then I think - geez, she could do a lot in 30 minutes. When I went in to check a few seconds ago, she told me her stomach hurts and I immediately try to figure out what she ate or how she hurt herself. I don't like that. I'm torn on giving her medicine, because I now have a fear of her knowing where the medication is...and she does know. Crap...DH isn't home or I'd probably be out buying a full set of locks. Docs seem to think it's just a stage - since much of her previous behavior is not getting the desired results (as I do a better job at my parenting) - she had to move on to bigger and better. I just can't get into this 'ignore it' mode. I'm scared. Truthfully, she hasn't scared me in a long time...and now I'm obsessing. I don't even know what to tell her when I go to check on her. I don't want to say "I'm making sure you aren't hurting yourself"...but I don't have anything to say that would sound remotely true because I don't normally do it. Just something about her attitude tonight - her expression is different. I'm going back in...