Sound weapon

Sonic weapons, developed after Al Queda's attack on USS Cole off Yemen, could be used to deter would-be aggressors. The High pitched warning tone generated by the weapon can cause nausea or fainting, while people outside the beam remain unaffected.
The weapon, a long range acoustic device (LRAD), is loudhailer and warning system that allows military and police authorities to control crowds and clear buildings. It can provide amazing voice and tone clarity in a 15 to 30 degree beam at distances over 300 metres using only two amperes of power. In addition to microphone input, it can communicate in various languages via the built in MP3 player or phraselator.
Two ultrasonic wawes generated by the weapon travel at slightly different frequencies and combine on meeting the target object or person to reproduce original sound with almost no loss of clarity.