The capital military police and the border patrol have both inquired about using these millimeter wave weapons. Both were rejected [1]. The weapons were considered but also rejected for use in Iraq and Afghanistan [2].
In 2010, a prison made news by installing such a weapon, a move opposed by the ACLU [3]. It is unclear if it was ever used.
[1] https://www.npr.org/2020/09/16/913748800/military-police-lea...
[2] https://news.yahoo.com/the-secret-troubled-history-of-the-mi...
[3] https://www.aclu.org/news/national-security/dont-let-militar...
“It works by heating the water molecules in the top 1/64-of-an-inch layer of the skin,” said Marine Corps spokesman Maj. David Andersen.
According to reports, a 2-second burst from the system can heat the skin to a temperature of 130° F. Elsewhere, the AFRL describes the sensation as similar to touching an ordinary light bulb that has been left on for a while. “Unlike a light bulb, however,” says the AFRL fact sheet, “active-denial technology will not cause rapid burning, because of the shallow penetration of the beam and the low levels of energy used.”
Edit (me, not the article): I'm not saying that this information is necessarily true, this is just some info I found that was at the top of the search results, from 22 years ago, that I put no effort into fact-checking with other sources. And I wouldn't be surprised if they're used for crowd control, but I don't know. But the second half of the parent comment seems to be accurate.
After all the skin layers are gone, it's not like the beam will stop working... :/
> Edwards said some of these items are being developed by companies looking “to make their mark in the industry”.