From the New York Times:
The police fired a sound cannon that emitted shrill beeps, causing demonstrators to cover their ears and back up, then threw tear gas canisters that released clouds of white smoke and stun grenades that exploded with sharp flashes of light. City officials said they believed it was the first time the sound cannon had been used publicly. “Other law enforcement agencies will be watching to see how it was used,” said Nate Harper, the Pittsburgh police bureau chief. “It served its purpose well.”
