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:
- 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.