Hegseth approves testing of "heat ray" at the border. Here's how it works
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Defense Secretary Pete Hegseth attends a meeting between President Trump at the White House on July 21. Photo: Aaron Schwartz/CNP/Bloomberg via Getty Images
Defense Secretary Pete Hegseth has approved testing of a military-grade "heat ray" for potential use along the U.S.-Mexico border — a weapon that uses invisible energy beams to produce an intense burning sensation on human skin.
Why it matters: The potential use of a military weapon against migrants raises significant safety and legal questions, including whether the technology could cause injuries or endanger people attempting to cross the border.
Driving the news: CNN reports that Hegseth approved a seven-month loan of the Active Denial System to DHS, allowing the agency to test the weapon and develop tactics for its potential use at the border.
- The authorization doesn't mean deployment. It remains unclear if DHS will ultimately use the weapon.
What they're saying: A Customs and Border Protection spokesperson tells Axios: "CBP is continually evaluating new technology, especially technology that can save lives while simultaneously enhancing national security effectiveness."
- Patrick Weaver, Hegseth's deputy chief of staff, commented on the testing in an X post: "The border is now a military installation and a battle lab for testing new systems, to include directed energy weapons," he wrote. "The border is locked down!"
Here's what to know about it.
What to know about the Active Denial System heat ray
How it works: The weapon — which has a range of up to 1,000 meters — fires an invisible beam of electromagnetic energy that penetrates roughly 1/64 of an inch into the skin, rapidly heating its surface and triggering an intense burning sensation, according to the Department of Defense.
- Officials compare the sensation to the blast of heat felt when opening a hot oven, saying it is intense enough to trigger an almost instantaneous reflex to flee.
- The burning sensation stops when someone moves out of the beam, though a residual tingling or tenderness can linger for 10 to 15 minutes, according to the Pentagon.
Can the heat ray hurt people?
Per the DOD, the device was specifically designed to be nonlethal.
- For it to actually kill someone, the DOD says exposure "would have to be sustained and prolonged many times over the duration required to achieve the repel effect."
Yes, but: The weapon has caused second-degree burns in at least two documented incidents. A laboratory accident in 1999 left one person with a blister, while an airman suffered burns during a 2007 training exercise after procedural errors led to overexposure. The airman made a full recovery.
- The Pentagon says controls, operating procedures, checklists, software upgrades and training reduce the risk of injury.
Has the heat ray been considered for border use before?
The idea of using directed-energy weapons at the border isn't new.
- The Air Force began researching the technology in the late 1980s, and the Pentagon developed the Active Denial System as a military demonstration project from 2002 to 2007.
In 2018, former DHS Secretary Kirstjen Nielsen rejected a proposal to use the technology against migrants, CNN reports.
- In July 2025, the Pentagon's Joint Intermediate Force Capabilities Office published an article that argued in favor of using energy weapons — like "active denial technology" — to enforce border security.
What they're saying: Jared Keller, author of the Laser Wars defense technology newsletter, says the weapon has raised ethical and legal questions since its development because it is designed to inflict pain on people.
- "Whether this means it's an appropriate tool to deploy at the southern border or not depends on your interpretation of those effects," Keller tells Axios. "Personally, I simply would not do this."
- Keller says that this move is another sign of how the U.S. has turned the border into a "battle lab" to test new tech. He pointed to high-energy lasers, microdrones and futuristic heads-up displays as examples.
