Right, but the one that actually causes a painful sensation that was referred to earlier uses RF energy and is basically a targetable micro-wave oven. That one is called the Active Denial System.LRAD=Long Range Acoustic Device.
I'm not sure if it was already mentioned in this thread, but it was used in 2005, successfully.
http://www.foxnews.com/story/0,2933,174921,00.html