An LRAD device, the large black speaker in the top left, deployed by the New York Police Department.
Chicago police have purchased two "Long Range Acoustical Devices" -- sound cannons -- in preparation for the thousands of protesters at the NATO Summit.
"We never had that before in Chicago," Supt. Garry McCarthy said Tuesday. "I've been talking about how we've learned from what's happened at these events in other cities and other tactics and strategies that other departments have used, and we've gotten better at it and better at it and better at it."
LRADs are equipped with a shrieking alarm able to send pain-inducing sound waves of up to 150 decibels that can be heard as far as 1,600 feet away, according to The Guardian. The use of the sound cannon is controversial since the human threshold for pain lies between 110 and 120 decibels.
But Chicago's top cop said the plan, however, isn't to use the devices that way, but rather to send "clear, crisp" messages to demonstrators.
"We're not going to be in the business of dispersing crowds and have people running all over the place. People who are committing crimes are going to be arrested and extracted from the crowd. That's the strategy we are going to use," he said.
Sound cannons were first used by the police at the 2009 G20 summit in Pittsburgh to control protesters.
They were also used in 2011 at the Super Bowl and at various Occupy events, according to the Huffington Post.
The sound cannons were purchased for $20,000 each and have 15 different messages already recorded for Chicago police to use.