[Sandy]

The higher sound level horns are also generally higher pitched.
So while being loud,
they don't get much attention.
There are a set of horns at the auto store from WOLO (and others)
that are 125 dB.
One horn is high pitch, the other low.
Together they have that great old Buick sound.
Mine are wired so the high pitch 'beeps' normally,
and they both go on if the brakes are applied.
This gives the big sound when needed,
but the friendlier high pitch when you want to just beep Hi.
I've done this on my motorcycles and in my car.
works great and that dual tone gets noticed.

Tech note,
older people don't hear the hi pitch very well,
it takes twice the power to raise the level 3 dB (ie 125 to 128)
but it takes 10 dB more to sound louder to the ear.