LRAD

A long-range acoustic device (LRAD), acoustic hailing device (AHD), or sound cannon is a specialized loudspeaker and sound weapon that produces sound at high power for communicating at a distance. It has been used as a method of crowd control, which has historically been known to cause permanent hearing damage over long periods, having an extremely high decibel capacity. Other uses have included for negotiations in siege situations; to deal with piracy at sea; for mass notification during natural disasters or other emergencies; and by the military, including several navies.