90% of aftermarket alarms are apparently installed with the noise- and vibration-detectors turned all the way up, presumably so the person buying them will feel like they got something for their money. The result is continual false alarms.
I don't know why anyone buys an alarm system anymore. After years of getting a 3 am alarm serenade I have to say my first reaction upon hearing a car alarm is *not* that someone must be stealing the car. Someone needs to invent an EMP gun that can take these little noisemakers out at fifty paces. ;)