In the afternoon, protesters who tried to march toward the convention center where the gathering was being held encountered roaming squads of police officers carrying plastic shields and batons. The police fired a sound cannon that emitted shrill beeps, causing demonstrators to cover their ears and back up; then the police threw tear gas canisters that released clouds of white smoke and stun grenades that exploded with sharp flashes of light.That's from this story in the New York Times.
City officials said they believed it was the first time the sound cannon had been used for crowd control. “Other law enforcement agencies will be watching to see how it was used,” said Nate Harper, the Pittsburgh police chief. “It served its purpose well.”
The Washington Times reported back in March, 2004:
The equipment, called a Long Range Acoustic Device, or LRAD, is a "nonlethal weapon" developed after the 2000 attack on the USS Cole off Yemen as a way to keep operators of small boats from approaching U.S. warships.
Now the Army and Marines have added this auditory-barrage dispenser to their arms ensemble. Troops in Fallujah, a center of insurgency west of Baghdad, and other areas of central Iraq in particular often deal with crowds in which lethal foes intermingle with civilians.