Where I live, it wasn't illegal for me to change the locks, and it wasn't illegal for him to try to break the door down in front of the police, because his name was on the deed. HOWEVER, he didn't know that part. AND, because he was doing drugs, the threat that, if we went to court over it, he may be ordered to take a drug test scared him enough to stop any problem.
I had to learn when to push the envelope because he was pushing it a lot harder. Once he realized I had him figured out, things changed. As for the car alarm, at one point I slept with my keys and pepper spray by my bed.
I think being afraid of the other person is part of the process that many recovering "friends of alcoholics/addicts go through.
Good luck with whatever you decide to do.