The New York Police Department is testing a new device it says can detect firearms concealed beneath layers of clothing, a high-tech crime-fighting tool seemingly torn from the pages of science fiction, reports the Wall Street Journal. The so-called T-Ray machine detects terahertz radiation, a high-frequency electromagnetic natural energy that is emitted by people and can penetrate many materials, including clothing. "If something is obstructing the flow of that radiation, for example a weapon, the device will highlight that object," said Commissioner Raymond Kelly, who described the device Wednesday in a speech.

News of the device prompted concerns from privacy advocates, though they also saw a potential benefit: It might render unnecessary the legally disputed police policy of stopping and frisking people who haven't been first identified as suspects in crimes. In an image displayed by Kelly, the T-Ray scanner highlighted the body of a plainclothes officer in neon green—with a gun clearly visible as a black shape. The image was captured with the officer standing about 30 feet away. Kelly said the department received the machine last week. It is manufactured by Digital Barriers and was paid for by the U.S. Department of Defense.