Karl2500

I once rigged one of those small "stadium" air horns by taping a popsicle stick from the front of the horn to the botton of the can. Then I wrapped several thick rubber bands from the horn to the bottom of the can. I then zip-tied the horn to the inside door handle, closed the door, and carefully zip-tied the center of the stick to the seat frame. then I crawled out the passenger side door. This could work on the outside of the car by mounting the horn to a bumper and use fishing line to a telephone pole or whatever.

lots of fun at crouded places, School, police stations, church etc.
not so good late nite in quiet neighborhoods