According to Arizona law, a car horn is only to be used in an emergency.
Arizona state statutes (28-954) spell out: "If reasonably necessary to ensure safe operation of a motor vehicle, the driver shall give an audible warning with the driver's horn but shall not otherwise use the horn when on the highway.”
(For state law, "highway" means any road, street or public way, said Officer Joy Craig, a DPS spokeswoman.)
A driver can receive a ticket for any honking that is not done in an emergency situation, e.g.
sitting in a car and honking for someone to leave a house is illegal.
Some legal uses of honking would be:
Warning someone who is ready to run in front of your vehicle.
Warning someone who is changing lanes that your vehicle is in their blind spot.
The purpose of this law is to avoid road rage and unnecessary noise.
“Road Runner’ A little-known law: Honking often illegal. Arizona Daily Star. February 16, 2009. Page A14.