http://www.slate.com/blogs/future_tense ... ntrol.html
On Wednesday afternoon, a peaceful demonstration in Ferguson, Missouri, about Michael Brown's killing turned into a standoff between protesters and law enforcement, and eventually devolved into chaos.
Most of these crowd-control tactics are, unfortunately, familiar, whether you've personally encountered them or just heard about their use. But what's a noise-based weapon? The ones used in Ferguson are called LRAD sound cannons, or Long Range Acoustic Devices, and they allow for very serious crowd control.