This may also be of interest to people - emulating a car horn for bikes https://loudbicycle.com/

(of course, there's also the locomotive horn, but the equipment required is a bit impractical - https://www.youtube.com/watch?v=XTQSWtK65PE)

I use the loud bicycle horn on my daily rider, it’s excellent. Car drivers actually respect it. Prevents right hooks

Or this: https://www.amazon.com/gp/product/B000ACAMJC (compressed air).

I've periodically toyed with the idea of adding a locomotive horn to my motorized vehicle, but I'd be afraid that using it would cause an accident.