That movie got me thinking, because it makes a number of claims about car alarms that jive with my personal feelings about them. They're noisy, obnoxious, tend to go off at night, and are almost universally ignored by passersby, people in nearby houses, and the car owners themselves. Despite these flaws, having one is almost default for new automobiles, and you even get a discount on insurance if you have one.
So the question is: Do car alarms actually reduce the incidence of theft of or from automobiles in which they are installed? If so, by how much? Whether or not the reduction (if any) is worth the hassle and noise will, of course, be a matter of opinion.
Edit: I'm not, of course, referring to car security systems in general. I'm only questioning the usefulness of the loud noise making aspect of them.