The Active Denial System (ADS) is a non-lethal, directed-energy weapon developed by the U.S. military, designed for area denial, perimeter security and crowd control. Informally, the weapon is also called the heat ray since it works by heating the surface of targets, such as the skin of targeted human subjects.

ADS emits a beam of electromagnetic wave with frequency of 95 GHz to a subject. When the waves touch the skin, the wave energy is transformed into heat in contact with water molecules of the skin. A pulse of 2 seconds would heating the skin to a temperature of about 55 ° C, causing a very intense sensation of burning pain. It would take 250 seconds of exposure to the beam to burn the skin

The Advanced Denial System is considered as a electromagnetic radiation weapon.

The ADS was developed in secret for 10 years at a cost of 40 million US dollars. Its existence was revealed in 2001, but most of the details on the effects of ADS on humans remain classified.