Essentially, it's a microwave emitter tuned to a frequency that triggers human nerve endings. The industrial-strength model can do so from half a mile away.
This is supposed to be a "humane" weapon, like tear gas or a fire hose, in that it does not (usually) cause lasting harm to the people it is used on. That is, I suppose, a reasonably noble cause.
However, consider the implications of a device that can cause unbearable pain without leaving a mark. Also consider what kind of people might want to do precisely that. It doesn't even sound bad, does it?
"They turned on a box and all of a sudden I was in this terrible, burning pain."
"But they didn't actually hurt you, right? There is no lasting damage?"
"In point of fact, you can't provide any evidence that you were tortured at all, can you?"
This is one of those things I think we will end up wishing we could un-invent.
Run away the ray-gun is coming : We test US army's new secret weapon | the Daily Mail