last night after i closed my car i usually leave my windows slightly down as i have rain visors on windows ,for some strange reason my alarm went off ,this has never happened before ,there was no one around ,what could have possibly trigered this as i park in this garage every night

 

I would like to know exactly how our alarms work and what they're capable of.

My 2002 BMW had the following:

Ultrasonic motion sensor for interior--any movement inside will trigger alarm
Hood/doors/trunk sensor--any opening while armed triggers alarm
Tilt sensor -- any change of the vehicles ride height as if someone is lifting the car or trying to steal the wheels will trigger the alarm. This came in handy once as a tow truck driver WRONGLY tried to tow my BMW away. He put the wheel jack on the rear and as soon as he started pumping it my alarm wailed. I ran outside and stopped his @$$. He dented my side skirt and made them pay up.

I assume our alarms will go off when you open any of the doors/hood/trunk... but not sure of the other two. Anyone know?

If your car is going off randomly though its surely a faulty sensor unless our cars do detect motion.