Cal. Codes » Vehicle Code / DIVISION 12. EQUIPMENT OF VEHICLES / CHAPTER 5. Other Equipment / ARTICLE 1. Horns, Sirens and Amplification Devices
California Codes

Cal. Vehicle Code § 27001 (2026)

✓ current as of May 2026
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(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.

Notes of Decisions
Cited in 8 cases (3 in the last 5 years), 1962–2023 · leading case: Susan Porter v. Kelly Martinez, 68 F.4th 429 (9th Cir. 2023).
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Susan Porter v. Kelly Martinez, 68 F.4th 429 (9th Cir. 2023). · cites it 7× “Cal. Veh. Code § 27001 . Plaintiff was cited for misuse of a vehicle horn under Section 27001 after she honked in support of protestors gathered outside a government official’s office.”
Porter v. Gore, 354 F. Supp. 3d 1162 (S.D. Cal. 2018). · cites it 3× “Curiel, United States District Judge When a protestor sounds her car horn at a political rally, does she engage in constitutionally-protected speech, or does she properly put herself in the crosshairs of California Vehicle Code § 27001, the so-called "horn ordinance?" The…”
Dominic Garcia v. Nat'l Labor Relations Bd., United Parcel Serv., Intervenor-Respondent, 785 F.2d 807 (9th Cir. 1986). “…Code restricts the use of a horn to occasions when it is necessary for safe operation or as a theft alarm system. Cal. Veh.Code § 27001 (West 1985).”
Menchaca v. Helms Bakeries, Inc., 439 P.2d 903 (Cal. 1968). “. .” (Italics added.) Hence defendant was adequately warned that plaintiffs contended that equipage of the truck constituted an issue for trial.”
Susan Porter v. Kelly Martinez (9th Cir. 2023). · cites it 7× “Cal. Veh. Code § 27001 . Plaintiff was cited for misuse of a vehicle horn under Section 27001 after she honked in support of protestors * The Honorable Edward R.”
Porter v. Gore (S.D. Cal. 2021). · cites it 3× “1) Plaintiff Susan Porter 2 challenges Section 27001 as a law that violates her First Amendment rights by preventing 3 or deterring her from using her horn to express her approval at a public demonstration.”
Porter v. Gore (S.D. Cal. 2020). “25 Additionally, upon the Court’s own review of RFP Nos.”
Milloway v. Griffin Bldg. Material Co., 199 Cal. App. 2d 198 (Cal. Ct. App. 1962). “By analogy, we note that section 27000 of the Vehicle Code requires all motor *206 vehicles when operated on a highway to have a horn audible 200 feet, but does not require it to be sounded when the vehicle is backing, sounding of the horn being required when reasonably…”
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