Va. Code § 46.2-1060
It shall be unlawful for any vehicle to be equipped with or for any person to use on any vehicle any siren or exhaust, compression or spark plug whistle, or horn except as may be authorized in this title. It shall be unlawful for any vehicle operated on a public highway to be equipped with any warning device that is not of a type that has been approved by the Superintendent. It shall further be unlawful for any person at any time to use a horn otherwise than as a reasonable warning or to make any unnecessary or unreasonably loud or harsh sound by means of a horn or other warning device. However, vehicles of common carriers or extraordinarily large and heavy vehicles may be equipped with such type of warning device as the Superintendent may require or permit.
Notwithstanding the provisions of this article, a siren, bell, or supplemental horn may be used on a vehicle as a noisemaker for an alarm system if the device is installed so as to prohibit actuation of the system by the driver while the vehicle is in motion.
Va. Code § 46.2-1060