Sound weapons used on G20 protesters. On the live G-Infinity Indymedia broadcast, what sounds like the distinct oscillating chirp of the Long Range Acoustic Device (LRAD) military technology was overheard. The Active Denial System has not previously been used by law enforcement or military personnel at major demostrations in the United States until now (An LRAD system was on the streets at the 2004 RNC but not used). LRAD type systems can be used as loudspeakers and also to create extremely high-decibel “chirping” noises — which seemed to be heard on the broadcast. The LRAD was used recently to suppress dissent at large demonstrations in the nation of Georgia.
In addition this should raise questions about the role of the US Northern Command (NORTHCOM) which is developing civil dissent repression techniques for implementation around the country. NORTHCOM and the National Geospatial Intelligence Agency (NGA) have major roles in National Security Special Events (NSSE) — the NGA is providing geographic intelligence (GEOINT) to law enforcement under a special confidential agreement that gives them a “loophole” around the Posse Comitatus law restricting domestic military activity.
http://en.wikipedia.org/wiki/Active_Denial_System