well i came across this about horns on cars and what the law is here in Arizona.
Since i told my buddy’s im doing a roof mount they all say your just asking to be pulled over. I say its not illegal to have them on your vehicle, even in plain sight, but its debatable on blowing them, and i show them this.
“Any horn or other warning device shall not emit an unreasonably loud or harsh sound or a whistle.” that’s all it says
look for yourself,
http://www.azleg.gov/FormatDocument.asp?inDoc=/ars/28/00954.htm&Title=28&DocType=ARS