Montana Title 61. Motor Vehicles § 61-9-401. Horns, security alarms, and warning devices

(1) A motor vehicle when operated upon a highway must be equipped with a horn in good working order and capable of emitting sound audible under normal conditions from a distance of not less than 200 feet. A horn or other warning device may not emit an unreasonably loud or harsh sound or a whistle. The driver of a motor vehicle shall when reasonably necessary to ensure safe operation give audible warning with the horn but may not otherwise use the horn when upon a highway.

(2) A vehicle may not be equipped with and a person may not use upon a vehicle a siren, whistle, or bell, except as otherwise permitted in this section.

(3) A vehicle may be equipped with a security alarm signal device that cannot be used by the driver as an ordinary warning signal while the vehicle is in motion.

(4) An authorized emergency vehicle may be equipped with a siren, whistle, or bell capable of emitting sound audible under normal conditions from a distance of not less than 500 feet and of a type approved by the department. The siren may not be used except when the vehicle is operated in response to an emergency call or in the immediate pursuit of an actual or suspected violator of the law, in which event the driver of the vehicle shall sound the siren when reasonably necessary to warn pedestrians and other drivers of the vehicle's approach.