Fri Sep 25, 2009 at 09:17:30 AM PDT
I couldn't help but notice a photograph on Page A16 of today's Washington Post showing demonstrators against the G-20 meeting in Pittsburgh running away from "an ear-splitting siren" used by the police to disperse protesters.
The Washington Post story mentions "sound cannons".
Here's more mention in an AP report:
The marchers did not have a permit and, after a few blocks, police declared it an unlawful assembly. They played an announcement over a loudspeaker ordering people to leave and then police in riot gear moved in to break it up. Authorities also used a crowd-control device that emits a deafening siren-like noise, making it uncomfortable for protesters to remain in the area.