Actually California is one of the states which have specific rules about which horns are legal and which horns aren't and they have a fine schedule for violations. They also have statutes on the books about how you can legally use your horn and what constitutes illegal horn use.

So-called "train horns" have been receiving a lot of press over the past few years. In California big rigs and trash trucks (and authorized emergency vehicles) can attach them to their vehicles and use them as horns, but only if they're powered by air and connected to the air brake system of the truck. Even then, these horns must conform to state standards and be legally certified by the State of California.

~ Jon
1952 1/2 ton with 1959 235 | T5 with 3.07 rear end