U.S. Defense Secretary Pete Hegseth has given the Department of Homeland Security (DHS) permission to test a nonlethal heat ray weapon for possible use combating illegal immigration across America's southern border.
The Republican politician reportedly signed a memo in September which gave DHS permission to test the Active Denial System (ADS), which fires invisible electromagnetic waves that are absorbed close to the skin’s surface, producing a burning sensation compared to "an intensified version of opening an oven."
It is on the U.N. Special Rapporteur on Torture’s prohibited equipment list and deploying it on the southern border would likely trigger renewed discussion about border security and human rights.
President Donald Trump has made combating illegal immigration across the U.S.-Mexico border one of the main policy priorities of his second term in office.
In a statement to Newsweek, a U.S. Customs and Border Protection (CBP) spokesperson said: "CBP is continually evaluating new technology, especially technology that can save lives while simultaneously enhancing national security effectiveness."
DHS referred Newsweek to the CBP statement. A Pentagon spokesperson referred Newsweek to DHS when approached for comment.
How Does the Active Denial System Work?
The ADS is a vehicle-mounted energy weapon that produces electromagnetic waves around 95 GHz. Work on the technology was launched in the late 1980s by the U.S. Air Force, with the ADS established as a demonstration project from 2002 to 2007.
These waves, that are invisible to the naked eye, can be directed at targets around 1,000 meters away, according to the U.S. military.
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The beams are designed to be absorbed close to the skin’s surface, at depths of 0.3 to 0.4 millimeters, causing a rapid rise in temperature.
This triggers sensory nerve endings called nociceptors, producing what one Air Force technical sergeant called "an intolerable heating sensation on the skin."
Speaking in 2007, Staff Sergeant Jason Delacruz, an ADS operator, said: "The pain is comparable to an intensified version of opening an oven and feeling the initial blast of hot air.
"The effects are extremely sudden, and natural instincts automatically force you to quickly exit the target area."
The military says the intense heating sensation stops when the beam is switched off or the person moves out of its path. Residual tingling or tenderness can last up to 15 minutes, according to a Pentagon account of a 2012 demonstration. Thus far, the ADS has not been actively deployed in either a combat or policing capacity.
Health Concerns
ADS is not intended to cause long-term damage, such as serious tissue injury, but there have been reports of second-degree burns and health concerns have been raised by groups, including the OHCHR.
According to Axios, in 2007 an airman received burns from an ADS after it was misused during a training exercise, though they made a full recovery. Another individual developed a blister from a laboratory accident involving an ADS in 1999.
In a 2023 report, the U.N. Special Rapporteur on Torture concluded the use of directed-energy weapons, such as the ADS, "should not be used in law enforcement" and "is widely considered to violate international human rights law."
It warned "a long exposure to this directed energy could potentially lead to serious injuries" and also said "the silent and invisible nature of the directed-energy beam makes avoidance of the weapon difficult, which could prevent people from dispersing safely and lead to panic-driven stampedes."
The report concluded: "Because of the intolerable pain they cause, their indiscriminate nature, and potential immediate and long-term health effects, they are on the Special Rapporteur on Torture’s prohibited equipment list until such matters can be resolved."
Testing by the Air Force published in 2008 concluded ADS waves "do not promote cancer or cause reproductive problems."
Speaking in 2012, Stephanie Miller, then head of the radio frequency bioeffects branch for the Air Force Research Laboratory, said: "We understand what the safety margins are, and in fact, these systems have been designed so that you can’t put enough energy on the surface of the eye in the time it takes a person to blink to cause damage to the eye."
What Has the Pentagon Agreed?
According to CNN, which first reported the memo, Hegseth approved the "temporary loan" of one ADS system for seven months, beginning in September, with DHS having sole responsibility for "system employment, use and development of tactics, techniques and procedures."
The memo says the loaned system "shall not be operated by DoW (Department of War) personnel," using the Trump administration’s term for the DOD. In 2025, Trump signed an executive order to rename the Department of Defense the "Department of War," though this hasn’t received the requisite congressional approval to make it official.
Citing a defense official, CNN said DHS will be able to request use of the ADS system "in border operations based on need" after the seven-month trial period.
Immigration Crackdown
Trump made cracking down on illegal immigration one of the main themes of his 2024 presidential election campaign. He declared a "national emergency at the southern U.S. border" almost immediately after returning to the White House in January 2025 and suspended nearly all asylum applications from certain countries.
The Trump administration also stepped up deportations, including to third countries such as Rwanda, and oversaw an aggressive Immigration and Customs Enforcement (ICE) campaign targeting people suspected of being in the U.S. illegally.
In 2025, unlawful crossings of the southern U.S. border fell to their lowest level in over half a century, according to DHS figures.
Newsweek's reporters and editors used Martyn, our AI assistant, to produce this story. Learn more about Martyn here.
Contact Newsweek editors on this story: Matthew Robinson and Oliver Pritchard.