Keying the car was totally bummer...however, as one who sat for 2 hours in my living room while a real estate person was off with a client and left his car at the property he was trying to sale that was across the street...I just called the Police, and they had the car towed. Pissed off the agent...and was very satisfying to me, and expensive to him.
All this to say I hate car alarms going off for no valid reason. Very rude. But, to quote a famous Jedi, there are alternatives!