Air horn: legal or illegal? yay or nay?

So my friend recently gave me an old two trumpet wolo air horn he found and I recently bought a vlair 88p air compressor. I kinda like how the air compressor is so portable so the only reason i'd mount it in the truck is if i put the horn in. It's a free horn and it sounds pretty awesome, but i dont want to waste the time to hard mount the air compressor if the horn isn't even legal on a personal vehicle.
Two questions:
1) is an air horn legal on a personal truck in california
2) since i'm pretty split on the idea, what is your guys' general opinion on the horn? yay or nay?

Note: I rarely use my stock horn to begin with so I'm not going to be one of those arseholes who's gunna honk the air horn every chance I get. Safety situations only (even then, most of the time my first instinct is just evasive driving)

 

Illegal as primary horn. I did one anyway. My buddy has the factory horn and a air horn.

 

so i'm guessing there's a switch in the cab to switch between the two?

 

Legal? Who cares. Fun to blast deserving people with...HELL YES!!! Mine is mounted under the bed right at ear level to people in cars. (and sitting on bus benches) It's just fun to watch un expecting jump when you blast them.

 

He put a seperate push button on the dash. He had air horns.

 

Mine played dixie

 

since when did we care about stuff being illegal?

 

It is legal. But you also need a electric horn to be legal.

I am a licensed class A commercial driver and a tractor trailer driver trainer.

Trucks with a air horn also must have an electric horn (referred to as a city horn). When the DOT or CHP preform an inspection they are only concerned with the operation of the electric horn.