The Active Denial System (ADS) is a 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 beings.
Sound like something out of a conspiracy nutjob’s imagination, but it’s actually real, and it’s terrifying.
That said, it’s still unknown what was used in Belgrade, Serbia a few days ago.