Riot police have begun deploying a non-lethal weapon called a long range acoustic device — LRAD, for short — against Occupy Movement protesters across the country. A controversial military device, which blasts targets with powerful sound waves capable of causing "extreme pain," the LRAD can sometimes even lead to permanent hearing loss. A tamer version of the device has been spotted during the recent evictions at New York's Zuccotti Park and Occupy Oakland's encampment. Here's what you should know:  

How does it work?
LRAD systems are used by airports "to sonically deter birds from residing in the paths of aircrafts," says Roberto Baldwin at Gizmodo. But in military situations, the LRAD is aimed like a beam to debilitate anyone within its 300-meter range with high-pitched frequencies.

What happens when the cannon is aimed at a human?
You might get a headache, feel extreme pain, or even lose your hearing. Think of it this way — a conversation in a restaurant is roughly 60 decibels. A dishwasher is 80. A live rock concert is 110. And "human discomfort" starts when a noise hits 120 decibels — imagine a chainsaw. Permanent damage starts at 130 decibels, and at 140 decibels, targets "could potentially lose their balance and be unable to move out of the path of the audio," says Baldwin. While a military-grade LRAD 2000X can go north of 160 decibels, Baldwin says police generally use a less potent version of the device, the LRAD 500X, which has the ability to blast out 110 decibels.

And LRADS have been used on Occupiers?
They have. In the clearing of protesters from Zuccotti Park earlier this week, the "NYPD descended on the park with deafening... LRAD noise cannons and several stadiums' worth of blinding Klieg lights," says Philip Gourevitch at The New Yorker. The NYPD denies that it used the device as a sound cannon with the intention of harming people, but instead used it as a megaphone. "We set it up away from where a crowd is," Police Department spokesman Paul Browne tells the New York Daily News. "We create a 50-foot safety zone. It sends out a clear, uniform message that can be heard for several blocks."

Sources: Gizmodo, Industrial Noise Control, New York Daily News, New Yorker