When I bought mine at a junk yard (Off a Ford for $ 5.00 USD), the clerk advised me to mount it vertically, somewhere near the center of gravity of the car. That way, a curb, speed bump, RR tracks, etc. won't set it off.how is it mounted? They need to be mounted so the sensor is in a certain position. The sensor is 2 axis, so it needs to be aligned such that the up/down axis is not going to trip it. It should be such that front/back and side/side will trip it.
With mine, it's got a red rubber cover, and it needs to be pointing up.