California Code, Penal Code - PEN § 20810

(a) Any person in this state who commercially manufactures or causes to be commercially manufactured, or who knowingly imports into the state for commercial sale, or who knowingly exports out of this state for commercial, dealer, wholesaler, or distributor sale, or who keeps for commercial sale, or offers or exposes for commercial, dealer, wholesaler, or distributor sale, any undetectable knife is guilty of a misdemeanor.

(b) Notwithstanding any other provision of law, commencing January 1, 2000, all knives or other instrument with or without a handguard that is capable of ready use as a stabbing weapon that may inflict great bodily injury or death that are commercially manufactured in this state that utilize materials that are not detectable by a metal detector or magnetometer, shall be manufactured to include materials that will ensure they are detectable by a metal detector or magnetometer, either handheld or otherwise, that is set at standard calibration.