A U.S. company is developing a microwave gun that can make people hear things. The Department of Defense sponsored project is thought to have military and crowd-control applications.

The device is based on the ‘microwave auditory effect’ or Frey effect named so after the scientists Allan Frey who researched it in the early 1960s. A modulated short-range signal beamed at someone produces shockwaves in the inner ear and makes him hear sounds that nobody else does. It was first discovered during WWII by crews operating radar.

The Sierra Nevada Corporation is working on a system called MEDUSA or Mob Excess Deterrent Using Silent Audio. It will utilise the Frey effect and make it into a feasible weapon.

The idea is to subject targets to microwave-induced ‘loud sounds’ that would discomfort or even incapacitate people. Since the beam is closely focused it would cause no harm to those not in the line of fire.

The company claims it will present a working prototype in about a year.

Experts say the concept is plausible, but the possible health risks must be studied before the gun is used. A powerful microwave emitter can cause serious damage to ears or brain reports the journal New Scientist.