Only a few hundreds protesters took to the streets of Pittsburgh to mark the opening day of the G20 summit of world leaders, but the police were taking no chances.
Sonic weapons or long-range acoustic devices have been used by the US military overseas, notably against Somali pirates and Iraqi insurgents.
But US security forces turned the piercing sound on their own citizens to widespread outrage. Pittsburgh officials said that it was the first time the "sound cannon" had been used publicly.
Please note this is very loud.
The sonic weapon appears to be more effective than the Metropolitan police's highly contentious kettling tactics used against G20 protesters in London. But it is equally controversial.
It is feared the sounds emitted are loud enough to damage eardrums and even cause fatal aneurysms.