321.433  Sirens, whistles, and bells prohibited.
  A vehicle shall not be equipped with and a person shall not use upon a vehicle any siren, whistle, or bell, except as otherwise permitted in this section. It is permissible but not required that any commercial vehicle be equipped with a theft alarm signal device which is so arranged that it cannot be used by the driver as an ordinary warning signal. Any 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 five hundred feet, but the siren, whistle, or bell shall 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, and the driver of the vehicle shall sound the siren, whistle, or bell when necessary to warn pedestrians and other drivers of the approach of the vehicle.
[C39, §5034.42; C46, 50, 54, 58, 62, 66, 71, 73, 75, 77, 79, 81, §321.433]
98 Acts, ch 1080, §4

For applicable scheduled fine, see §805.8A, subsection 3