Most American car horns beep in the key of F.

Train horns are usually chords. The more common ones being AMaj6,A7, C# dim7, and D#m.

The pitch of a typical foghorn is equivalent to B3 on a piano (the third-lowest “B” key)

Ships over 200 meters in length a required to have horns in the range of 70–200Hz. 70Hz is equivalent to the second lowest “C” on a piano.

The loudest car horn could be heard 9.3 miles away. It was actually a WWII Navy destroyer horn modified for a minivan.