> I can’t think of a single car that has been protected by a car alarm since they were invented.

Many insurance companies offer lower premiums if you install a car alarm. So I guess they work at least a little, otherwise they wouldn't lower their premiums.

It may not actually stop a thief, but it may get a thief to chose a car that doesn't have an alarm, or maybe it is just a correlation, but there is at least something.

Still, I think they should be made illegal, they are a nuisance, there are already laws against making excessive noise and car alarms should be included. And if they create an arms race, by getting thieves to prefer cars without alarms, that's even more reason to ban them.