Billed by its maker, Raytheon, as "a revolutionary, less-than-lethal directed energy application," the new Silent Guardian brings Flash Gordon-style ray-gun technology to today's wars of insurgency. And best of all: it leaves no marks.Traveling at the speed of light, the Silent Guardian's focused beam of "millimeter-wave" energy produces an intolerable burning sensation, "causing the targeted individuals to instinctively flee or take cover." Because it only penetrates the skin to 1/64th of an inch, the beam causes no lasting damage (other than the psychological sort).

Also known as extremely high frequency (EHF), millimeter waves -- which are slightly shorter in wavelength than microwaves -- have been used in radio astronomy and remote sensing. The Air Force has reportedly developed a wider-range version of the Guardian, known as the Active Denial System, which produces what researchers like to call "the goodbye effect."

Part of the Directed Energy Solutions program at Raytheon (which has requested that journalists not describe it as a "ray gun"), a tabletop version of the Silent Guardian was tested recently by Michael Hanlon, a reporter with the U.K. newspaper The Daily Mail. "This machine has the ability to inflict limitless, unbearable pain," Hanlon reported after momentarily feeling the beam on a fingertip. The "wave of agony" it unleashes has a range of more than 250 meters.

"I have been in front of the full-sized system and, believe me, you just run. You don't have time to think about it, you just run," Raytheon executive George Svitak told Hanlon.

One possible use of the Guardian is in crowd-control situations like those faced by the U.S. military in Iraq. "The system is available now and ready for action," Raytheon promotional materials state.