Active Denial System
U.S. directed-energy weapon using millimeter waves for crowd control.
The Active Denial System (ADS) is a directed-energy weapon built by the U.S. military for tasks like keeping people out of an area, guarding perimeters, and managing crowds. It’s often called a heat ray because it heats up whatever it hits, including human skin. The system was sent to Afghanistan in 2010 but was pulled out before it ever saw combat. Raytheon once sold a shorter-range version of the technology. The project was run by the Department of Defense Non-Lethal Weapons Program, with the Air Force Research Laboratory in charge.
The device shoots a 100-kilowatt beam of 95 GHz waves—about 3.2 millimeters long—at a target. This works like a microwave oven, but at a much higher frequency: microwaves use 2.45 GHz. The millimeter waves only go into the top layers of skin, about 0.4 millimeters deep, while regular microwaves can reach about 17 millimeters. The beam heats water and fat molecules in the skin instantly through dielectric heating. People feel the need to get away when their skin hits just over 44°C (111°F). First-degree burns happen around 51°C (124°F), and second-degree burns at about 58°C (136°F). In tests, pea-sized blisters—a sign of second-degree burns—showed up in less than 0.1% of exposures. The burns are like microwave burns but only on the surface because the waves don’t go deep. The skin keeps heating up as long as the beam is on, depending on the target’s material, distance, and the operator’s settings. Most test subjects felt pain within three seconds, and nobody could take more than five seconds. An Air Force Research Laboratory spokesman said that for the first millisecond it felt like warming up, then got hotter until it felt like fire, but the skin returned to normal and the pain stopped as soon as the beam was off.
Like any focused energy, the beam hits everything in its path, including what’s behind the target, without telling people apart. Anyone who can’t leave the area—like someone with a disability, a baby, or a person stuck—would keep getting hit until the operator stops. Reflective materials, like aluminum foil, can bounce the radiation away, so clothing made from them could offer protection.
After about 10,000 test exposures on volunteers, a Penn State Human Effects Advisory Panel said ADS is a non-lethal weapon that works well and rarely causes injury. They found no major issues for people wearing contacts, glasses,
- field
- Directed-energy weapon
- nationality
- United States
- known_for
- Non-lethal crowd control using millimeter wave heating
- developer
- U.S. Department of Defense Non-Lethal Weapons Program, Air Force Research Laboratory
- deployment
- 2010 in Afghanistan (withdrawn without combat)
Lore & Background
The Active Denial System (ADS) was developed under a Defense Department Advanced Concept Technology Demonstration Program from 2002 to 2007. It fires a 100 kW beam of 95 GHz waves (3.2 mm wavelength) that heats skin via dielectric heating, similar to a microwave oven but with shallower penetration. The effect repels humans at slightly above 44 °C, with first-degree burns at about 51 °C and second-degree burns at about 58 °C. In testing, pea-sized blisters occurred in less than 0.1% of exposures. Most test subjects reached pain threshold within 3 seconds, and none could endure more than 5 seconds.
In 2010, the ADS was deployed to Afghanistan but was withdrawn without being used operationally. On August 20, 2010, the Los Angeles Sheriff's Department announced intent to use it at Pitchess Detention Center for operational evaluation, such as breaking up prisoner fights. As of 2014, the ADS was only vehicle-mounted, though portable versions were being worked on by U.S. Marines and police. Raytheon marketed a reduced-range version. In 2014, reports indicated Russia and China were developing their own versions.
Safety studies included approximately ten thousand test exposures. A Penn State Human Effects Advisory Panel concluded ADS is non-lethal with high effectiveness and low injury probability. Studies found no significant effects on eyes, cosmetics, age differences, or male reproduction. One airman in 2007 received second-degree burns on both legs from an overdose; a 1999 lab accident caused a small second-degree burn. Long-term effects were deemed unlikely, though overexposure could cause thermal injury with a very low cancer risk from scars.
Reader's Guide
The Active Denial System represents a significant development in non-lethal weaponry, offering a means of area denial and crowd control without causing permanent injury in most cases. Its deployment in Afghanistan, though unused, and consideration by law enforcement highlight its intended role in reducing lethal force. The system's mechanism—heating skin with millimeter waves—raises ethical and practical questions about discrimination, as the beam affects all matter in its path, including those unable to flee. The low incidence of burns (less than 0.1% of exposures) and independent safety reviews support its classification as non-lethal, but the potential for overexposure and the need for operator exceptions to RF exposure limits underscore ongoing concerns. The development of similar systems by Russia and China indicates the technology's global interest. The ADS's legacy lies in its demonstration of directed-energy for non-lethal purposes, balancing effectiveness against the risk of injury, and its influence on future crowd-control and perimeter-security technologies.
Did You Know?
- The ADS uses a 100 kW beam of 95 GHz waves, corresponding to a wavelength of 3.2 mm.
- Most human test subjects reached their pain threshold within 3 seconds, and none could endure more than 5 seconds.
- Pea-sized blisters occurred in less than 0.1% of approximately 10,000 test exposures.
- Reflective materials such as aluminum cooking foil can be used to make protective clothing against the radiation.
More in American inventions 1-24
Spotted an error? Know more?
This is a living reference — every entry is fact-audited, and reader corrections feed straight into our audit queue. Suggest an edit · See this site's audit record