by the way, for those who have not experienced it, checking locks goes like this:
park the car. get out. lock the door. walk to the building. wonder if you remembered to lock the car. go back, check the locks.
or, you're ready for bed, so you make the rounds, front door, back door, porch door. lock everything. go upstairs, read, etc., start falling asleep and then think "did I lock the doors?" you know you already checked it, but on the other hand, that could have been a different night you are remembering. go back, check it. this happens night after night, so you know it is obsessive, and you know you already checked the locks, so you get mad and try to tell yourself "this is stupid! I'm not going back down!" but you also wonder if you really locked the doors...
When it got really bad, I would have to squint at the lock and try to force myself to put it in my memory that it really was locked. This did not necessarily work.