Liberty Times, compiling reports from The Guardian, CNN, The Washington Post and The New York Times, said the Guardian reported the matter on Oct. 22, with CNN first obtaining the memo. The device is the Active Denial System (ADS), popularly called a ‘heat ray’. Official US usage now says ‘War Department’; this article uses ‘defense secretary’ throughout.

Under the memo, the system is ‘temporarily loaned’ to DHS for seven months from September, with extension possible. DHS is wholly responsible for deployment, use and developing procedures, and Pentagon personnel may not operate it. Where on the border and how it would be used has not been confirmed.

What the device is

A 2009 National Defense University case study says the system fires an energy beam that causes a strong burning sensation on the skin's surface. The reports say the 95 GHz beam penetrates only about 0.4 mm of skin and the effect, typically lasting 10 to 15 minutes, is temporary. The Marine Corps said in 2012 that the system complies with US international legal obligations.

Policy questions and history

Customs and Border Protection said it constantly evaluates new technology and values tools that can save lives. The Pentagon referred questions to DHS. The Washington Post reported the system went to Afghanistan about 20 years ago, was quickly brought back and never used in combat.

The New York Times reported it was weighed in 2018, under Trump's first term, to deter migrants, and The Washington Post said it was considered for protest control in 2020. It was not used either time. This time too, the scope of use, safety standards and outside oversight have not been made public.