The U.S. military has been working on several kinds of non-lethal crowd control over the years. There have been flash-bang grenades, noise and light arrays, and now the heat beam — or as the military likes to call it — the Active Denial System (ADS).
The device works by directing an electromagnetic beam at 95 gigahertz into unruly crowds. The resulting effect is likened to being "exposed to a blast furnace, with a sting thrown in for good measure" by Wired reporter Spencer Ackerman. The ADS is a weapon you don't see or hear coming, but when it hits you, your first instinct is to run.
After 11,000 test exposures, only two required medical attention, and neither resulted in serious harm. It isn't billed as a comfortable experience, of course. It has been questioned whether such a heat beam is safe — isn't it essentially cooking your skin like a microwave?
The difference is the radio frequency of the heat beam. The heat beam operates at the aforementioned frequency of 95 gigahertz and has a range of around 1,640 feet. This means any effects from the beam don't get very far into the body, though that range is quite a bit farther than other non-lethal deterrents used today.
Stephanie Miller, who measured the bioeffects of the system at the Air Force Research Laboratory explained to the Sydney Morning Herald that the beam is "absorbed very superficially." The beam only penetrates 1/64th of an inch, which "gives a lot more safety."
Microwaves on the other hand operate at a greater acceleration, which is what enables them to penetrate your food and cook it. So even though microwaves operate at one gigahertz, they go deeper, which is the important distinction here.
Nevertheless additional safety measures have been put in place. The beam operates on a three-second blast and then there is an automatic shut off incorporated into the device after that blast.
Currently the Active Denial System is only available to be mounted via vehicle, though portable versions are being planned. Curious about what it feels like? Wired's Ackerman braved the heat — Wiredtwice — and you can see him do it in the video below.