Car alarms are more annoying than helpful. Your first instinct is to turn it off not to check if a car is being stolen.. amirite?

Car alarms deter home burglars

I feel the same way about the flashing white lights that are the roofs of some school buses, largely because the light is flashing way too fast.

The point of a car alarm is that it draws attention. As annoying as it is for non thieves, a their does not want to draw attention to what they are doing. Also, car alarms are installed in such a way that the ignition is disabled. Usually somewhere deep inside the dash. So they are not going to get the car started.

Yeah but it makes everyone look, which makes the would-be thief run.

For real!! They are so annoying

You clearly live in a nice area if my car alarm goes off 9 times out of 10 someone is trying to get in to it