alarm system 2004 lincoln town car

car alarm just in the last 6 months have been randomly going off , have taken to
mechanic and they can't find a reason why its going off, even left car there a
week and it never went off but as soon as i took it back to my moms apartment
it started going off again, yes someone could be messing with it for whatever
reason but how can i stop this from keep going on and on, even disconnected
the horn and it went off again , had wiring checked for any shorts and nothing.
key fob wasnt programmed so waiting on new key fobs so any advise