27000.  (a) Every 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
which emits sounds that do not comply with the requirements of this
section.
   (b) Every refuse or garbage truck purchased after September 1,
1983, shall be equipped with an automatic backup audible alarm which
sounds on backing more than 36 inches and which 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 which is in good working order, located at the rear of the
vehicle and which 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) At the first scheduled overhaul for any refuse or garbage
truck, the operator shall consider equipping the refuse or garbage
truck not equipped in accordance with the requirements of subdivision
(b), with the alarm or device required under subdivision (b).



27001.  (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.


27002.  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.



27003.  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.



27007.  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.