I had a friend that was an avid train horn collector and restorer. He had 3 sets including a rare "5 bell" set and a 200 gallon air tank to run it all. The true horn honker guys DO NOT use them for scaring people or being annoying. They have "honk-offs" meeting up in a valley somewhere to listen to the echos from a well tuned set of horns. On a very rare occasion of being cut-off he might hit em to let them know he was there and rattle their windows for being stupid.
I might add that the other videos where you see they mounted them under the car will make them useless pretty fast when they get full of dirt and water.