This is the device that fills a car's interior with the throaty sounds of a sports car's V8 engine. Plugged into a car's DC adapter, it transmits "muscle" to a car's radio on an unused FM frequency. Synchronized to a car's alternator signal, its growling engine revolutions match a car's acceleration, producing the rumble of idle and the roar of redline for both automatic and manual transmissions. In top gear, its purring hum provides drivers the suggestion their conveyances are, for a brief period of time, undisputed masters of the road. Does not work with hybrid or electric cars. 5" L x 2" W x 2" D. (3 oz.)