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.

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