A riot policeman protecting the G-20 Summit stands guard in Pittsburgh, Pennsylvania. CHRIS HONDROS/GETTY IMAGES
A haze of tear gas rises above police at a gathering of students near Phipps Conservatory where world leaders were gathered for a dinner before the G-20 Summit in Pittsburgh, Pennsylvania. CHRIS HONDROS/GETTY IMAGES
ACOUSTIC WARFARE: The device seen on the top, called a Long Range Acoustic Device, concentrates voice commands and a car alarm-like sound in a 30- or 60-degree cone that can be heard nearly two miles away. It is about two feet square and mounted on a swivel such that one person can point it where it's needed. The volume measures 140-150 decibels three feet away - louder than a jet engine - but dissipates with distance. Read more about it here.
Left: A police officer holds the pin on a canister in Pittsburgh. Right: Police officers chase a protester in Pittsburgh. MATT ROURKE/AP
Protesters say police are too violent
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