The California Vehicle Code Section 27001 states

(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.

However, 95% of the times when I am startled by a car horn, the car is empty, and the horn has nothing to do with safe operation or a theft alarm system. Rather, the car is honking to let the owner know that he or she has just successfully locked the doors using a remote control - the so-called "honk-on-lock" feature.

Is this legal? Is it legal to sell a car which is configured to have this behavior? If not, why is the law not enforced? Would enforcement require additional legislative action? Proof of property damage?

  • Have you read Article 13? What does it say about this aspect of the "theft alarm system"?
    – user4657
    Mar 14, 2019 at 7:14

1 Answer 1


let's look at the referenced Section 28085

ARTICLE 13. Theft Alarm System [28085- 28085.] ( Article 13 added by Stats. 1977, Ch. 993. )

Any motor vehicle may be equipped with a theft alarm system which flashes the lights of the vehicle, or sounds an audible signal, or both, and which operates as follows:

(a) The system may flash any of the lights required or permitted on the vehicle.

(b) The system may sound an audible signal.

(c) No vehicle shall be equipped with a theft alarm system which emits the sound of a siren.

(Amended by Stats. 1994, Ch. 516, Sec. 1. Effective January 1, 1995.)

This tells us what is allowable as a theft alert system. It may use sound(b) and turn the car into a goddamned Christmas tree(a), provided it is not: a siren sound(c) not audible(b) or a non-permitted light like Emergency Vehicle Lights(a). It does not regulate when it may fire, only that the sound alert has to be audible (preventing infrasonic make-your-ears-bleed or dog whistle sounds) and that the lights have to be an allowable part of the vehicle. So you could set the alert to honk or play imperial march or berate the wannabe thief or use painful loud music, all provided that it is audible and does not violate other laws.

So, what is the correct operation of a car theft alert? Nothing in the article says, that you may just use the signals and honking for alerting in the case of theft, but that the system may use all the things in A and B under condition C to operate. Operation is "effect brought about in accordance with a definite plan". The definite plan for the alarm system is as follows:

  • initialize
  • alert the owner that it has correctly initialized
  • wait for theft attempt or shutdown
  • in case of theft: alarm everybody
  • in case of shutdown: shutdown

How the alertion and alarm are set up is up to the manufacturer's discretion, as long as the Article 13 is not breached.

Example: My Ford Fiesta does a double-flash of the turn lights and a low key beep overpowered by the lock operation on locking and a single flash on unlocking. That is the factory setup (for my area) afaik. The manufacturer (or if I wanted to go to a car shop) could under Article 13 set the activation to trigger a short honk or any other audible to signal proper initialization as part of the normal operation. The failure of the sound coming after locking the car would alert me that something is amiss and it is not operating. The top 3 causes are most likely that the car key battery might be dead, a malfunction of the car alert or someone jamming the frequency of the key.

As it is clearly part of the operation of the alert system, which is marked as a legal use of the horn of a car in Article 12 under Section 27001 b, yes, the alert may honk.

INAL, so only my layman reading.

  • Yes, I read the section on "theft alarms". Your interpretation seems creative to me... I think it is meant to describe the actual alarm going off. Otherwise where do you draw the line? Maybe whenever I honk my horn I'm just checking that an important piece of my alarm system is still working. Mar 14, 2019 at 9:21
  • 2
    @Metamorphic check what is considered proper as "operation" in law. The line is clearly that not I am honking, but the alarm is in operation
    – Trish
    Mar 14, 2019 at 9:23
  • Not getting it, sorry. In both cases a button is pressed that causes a sound to be made. In both cases the purpose is ostensibly to verify the functioning state of the alarm system. The word "operation" does not help me distinguish them... Mar 14, 2019 at 10:09
  • 4
    @Metamorphic in one case you press the button to trigger the horn with the intent to get a horn sound and test the horn that is part of the alarm. That is operating the horn. In the other you press a button to operate the alarm and the alarm makes a horn sound.
    – Trish
    Mar 14, 2019 at 10:13
  • 2
    You're telling the alarm to operate until told to be turn off. The alarm operates the horn itself to tell you it is now active. There's nothing complicated about this.
    – user4657
    Mar 16, 2019 at 9:06

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