They aren't legal and are probably more trouble than they are worth. I'd guess very foolish.

I have one in the van. I'm a bit paranoid about being hassled when I'm parked someplace overnight. I've figured if I turned it on the badguys might get nervous and it might attract attention. Never done it.

Someone called the police on a loud party down the block a few years ago. It was outside with much hootin' and hollarin'. I saw the car drive up, park alongside the party and hit the lights. Sat there a minute and drove away.

Broke up the party immediately without any more contact.