Pete Hegseth, the US secretary of defense, reportedly signed a memo last month permitting the Department of Homeland Security (DHS) to test a non-lethal “heat ray” for potential use at the US southern border.

The “heat ray”, known as the Active Denial System, is a military-grade weapon that shoots an energy beam causing “a sensation of intense heat on the surface of the skin”, according to a 2009 National Defense University case study on the weapon.

The sensation “creates an intolerable sensation and reflexive movement” such as ducking or running.

In a memo, first obtained by CNN, Hegseth authorized a “temporary loan” of the Active Denial System to the DHS for seven months beginning in September. The DHS can request further use of the Pentagon system if needed.

A spokesperson for Customs and Border Protection (CBP) said in a statement it was “continually evaluating new technology, especially technology that can save lives while simultaneously enhancing national security effectiveness”.

When asked for comment, the Pentagon referred the Guardian to the DHS, which shared the CBP statement.

It is unclear what the DHS plans to use the Active Denial System for exactly, but the memo permits the department to use it for potential operations at the US-Mexico border.

The US military initially brought the system to Afghanistan nearly 20 years ago, but it was quickly returned home without ever being used, the Washington Post reported.

Previously, CBP officials reportedly considered using the Active Denial System in areas with a large number of illegal crossings or for crowd dispersal, but it was never deployed.

When used, the Active Denial System can produce an invisible beam of 95 gigahertz that penetrates about 1/64th of an inch into the skin, causing a burning sensation. (The system is technically not a “heat ray” because it uses millimeter waves, not infrared, Forbes reported in 2020.)

Pentagon officials have compared the feeling to a blast of heat when opening a hot oven, according to CNN. The feeling is temporary, lasting between 10 and 15 minutes.

In 2012, the Marine Corps announced that the system was compliant with international legal obligations of the US, and officials said they felt “comfortable” that it was safe.

The new memo, seen by CNN, states that the DHS will be solely responsible for the system’s “employment, use and development of tactics, techniques and procedures”. It also states that no Department of Defense personnel shall operate it.

During the first Trump administration, officials sought to use the Active Denial System, first in 2018 to stop migrants from crossing the border, the New York Times reported. Later, in 2020, the administration also sought it to control protests in Washington DC after the killing of George Floyd, the Washington Post reported.