Article 1. Horns, Sirens And Amplification Devices of California Vehicle Code >> Division 12. >> Chapter 5. >> Article 1.

(a) A motor vehicle, when operated upon a highway, shall be equipped with a horn in good working order and capable of emitting sound audible under normal conditions from a distance of not less than 200 feet, but no horn shall emit an unreasonably loud or harsh sound. An authorized emergency vehicle may be equipped with, and use in conjunction with the siren on that vehicle, an air horn that emits sounds that do not comply with the requirements of this section.
  (b) A refuse or garbage truck shall be equipped with an automatic backup audible alarm that sounds on backing and is capable of emitting sound audible under normal conditions from a distance of not less than 100 feet or shall be equipped with an automatic backup device that is in good working order, located at the rear of the vehicle and that immediately applies the service brake of the vehicle on contact by the vehicle with any obstruction to the rear. The backup device or alarm shall also be capable of operating automatically when the vehicle is in neutral or a forward gear but rolls backward.
  (c) A refuse or garbage truck, except a vehicle, known as a rolloff vehicle, that is used for the express purpose of transporting waste containers such as open boxes or compactors, purchased after January 1, 2010, shall also be equipped with a functioning camera providing a video display for the driver that enhances or supplements the driver's view behind the truck for the purpose of safely maneuvering the truck.
  (d) (1) A construction vehicle with a gross vehicle weight rating (GVWR) in excess of 14,000 pounds that operates at, or transports construction or industrial materials to and from, a mine or construction site, or both, shall be equipped with an automatic backup audible alarm that sounds on backing and is capable of emitting sound audible under normal conditions from a distance of not less than 200 feet.
  (2) As used in this subdivision, "construction vehicle" includes, but is not limited to, all of the following:
  (A) A vehicle designed to transport concrete, cement, clay, limestone, aggregate material as defined in subdivision (d) of Section 23114, or other similar construction or industrial material, including a transfer truck or a tractor trailer combination used exclusively to pull bottom dump, end dump, or side dump trailers.
  (B) A vehicle that is a concrete mixer truck, a truck with a concrete placing boom, a water tank truck, a single engine crane with a load rating of 35 tons or more, or a tractor that exclusively pulls a low-boy trailer.

(a) The driver of a motor vehicle when reasonably necessary to insure safe operation shall give audible warning with his horn.
  (b) The horn shall not otherwise be used, except as a theft alarm system which operates as specified in Article 13 (commencing with Section 28085) of this chapter.

No vehicle, except an authorized emergency vehicle, shall be equipped with, nor shall any person use upon a vehicle any siren except that an authorized emergency vehicle shall be equipped with a siren meeting requirements established by the department.

An armored car may be equipped with a siren which may be used while resisting armed robbery. At all other times, the siren shall not be sounded. The authority to use a siren granted by this section does not constitute an armored car an authorized emergency vehicle, and all other provisions of this code applicable to drivers of vehicles apply to drivers of armored cars.

No driver of a vehicle shall operate, or permit the operation of, any sound amplification system which can be heard outside the vehicle from 50 or more feet when the vehicle is being operated upon a highway, unless that system is being operated to request assistance or warn of a hazardous situation. This section does not apply to authorized emergency vehicles or vehicles operated by gas, electric, communications, or water utilities. This section does not apply to the sound systems of vehicles used for advertising, or in parades, political or other special events, except that the use of sound systems on those vehicles may be prohibited by a local authority by ordinance or resolution.