Lt. Col. James G. Zumwalt, Retired Marine infantry officer :

It is time for law enforcement to introduce rioters to the 'crowd buster' – the Active Denial System.

https://www.wnd.com/2020/07/time-rioters-feel-burn-crowd-buster-tool

ADS is a directed-energy weapon system developed by Raytheon several years ago. It generates and focuses a high-energy millmeterwave radio frequency beam (a type of electromagnetic radiation) onto a target, causing a very hot, skin-surface burning sensation. This gives ADS the additional name of the heat ray, or pain ray.

ADS actually works similar to a microwave oven. There is one big difference, however; while the microwave cooks meat from the inside out, ADS only penetrates the skin's surface up to 1/64th of an inch. But that penetration is sufficiently unbearable to force any victim within the beam's path to immediately seek the nearest escape route. You will never see a snowflake move quicker to look for "safe space" than when targeted by ADS.

This system is one of the most effective non-lethal weapons designed to preserve perimeter security and crowd control.