Article 3.5. Headsets And Earplugs of California Vehicle Code >> Division 12. >> Chapter 5. >> Article 3.5.

A person operating a motor vehicle or bicycle may not wear a headset covering, earplugs in, or earphones covering, resting on, or inserted in, both ears. This prohibition does not apply to any of the following:
  (a) A person operating authorized emergency vehicles, as defined in Section 165.
  (b) A person engaged in the operation of either special construction equipment or equipment for use in the maintenance of any highway.
  (c) A person engaged in the operation of refuse collection equipment who is wearing a safety headset or safety earplugs.
  (d) A person wearing personal hearing protectors in the form of earplugs or molds that are specifically designed to attenuate injurious noise levels. The plugs or molds shall be designed in a manner so as to not inhibit the wearer's ability to hear a siren or horn from an emergency vehicle or a horn from another motor vehicle.
  (e) A person using a prosthetic device that aids the hard of hearing.