In January 2007, the U.S. Military brough a number of national and international journalists to a military base in Georgia to show off a revolutionary less-than-lethal technology designed to repel persons.
According to a report from the BBC, "Journalists who volunteered to be zapped during a demonstration on an air base in Georgia, described the sensation as similar to a blast from a very hot oven, too painful to bear and forcing them to dive for cover."
The system in use was reportedly similar to the Raytheon Silent Guardian protection system, a technology known generally as an "active denial system", or a "heat ray" and even as the "pain ray". The Raytheon unit, which focus its energy on an individual or apply to a broad area for crowd usage, employes millimeter wave technology, a similar technology to the detection systems being tested by the TSA which can see through clothing (read more on millimeter wave technology). The "heat ray" technology, says Raytheon can be used for both military or commercial purposes, including law enforcement, checkpoint security, force protection or general facility protection.
According to Raytheon, this is a "less than lethal" technology that can be used without causing injury. The unit is rather large, so don't picture Star Trek guns. The Silent Guardian unit is roughly the size of a Volkwsagen Beetle, and the unit also provides camera imaging so that operator can see their target as they control the system. Other versions have appeared as vehicle mounted, such as aboard a Humvee for battlefield situations.
More information: www.raytheon.com/products/silent_guardian/