During this week's anti-capitalist protests against the G20 summit in Pittsburgh, police used a 'sonic cannon' as well as CS gas to disperse demonstrators. The Long Range Acoustic Device emits an ear-splitting siren which is extremely uncomfortable to be around. Used previously against pirates off Somalia, this is the first time it has been used against civilians in the US. It is also currently being used by the military in Honduras .
The LRAD is manufactured by American Technology Corporation (ATCO), a San Diego-based company, which has also supplied it to the Chinese police. The company calls itself "a leading innovator of commercial, government, and military directed acoustics product offers" that offers "sound solutions for the commercial, government, and military markets."
There's a CrimethInc report of the Pittsburgh protests at Infoshop news