We also are going through the same thing. This has happened so many times, that I have lost count.
This a very hurtful situation to be in. You just can't trust them......they really need to earn the trust back.
Just recently, we have moved, we have no security system here to let us know if anyone opens an entry....so, we have to take care of that. That was a great idea to get your security system!
Our daughter is turning 17 in June and honestly, we really thought all this was behind us....we really thought she had made a change....until I found out she had a myspace, again, which we forbid.
I suggest if your daughter had a myspace, take a good look at her profile. You would be surprised at what these kids reveal about themselves. You will be able to see what they talk about, who her friends are, what they are up to.
We also took away our daughters cellphone, we took away her computer, we took away her tv, we just recently we through every single nook and crannie in her room and seached it....wow, was I surprised at what I found. We looked everywhere...under the mattress, in her pillowcases, behind bookshelves, under bookshelves, in her drawers, in her clothes...Everywhere.
Also, we had an officer come out and speak with her. Sometimes, that really does help. He also at the time told us, at 17, if she does not straighten us, we can emancipate her ( not sure if that is spelled right).
We told her this, not that I would do that, but, to really just try and give her a wake up call.
We have also made it clear, she is getting a job.
Teenagers are so hard, but, we just have to keep loving them, even if it means tough love.
Good luck to you and God bless ;0)