NEW YORK (AFP) - The New York Police Department (NYPD) already has the long arm of the law. Now, it gets X-ray eyes.

Officers are in the advanced stages of testing a futuristic new weapon in their war against gun-toting residents: a device that can detect the presence of hidden metal from a distance. The device measures terahertz, the natural energy emitted by people and objects.

"If something is obstructing the flow of that radiation, for example a weapon, the device will highlight that object," NYPD Commissioner Ray Kelly said in a speech on Thursday.

The boxy machine can be hidden in a vehicle, allowing officers to discreetly scan their target. The device is being seen as a possible alternative to the NYPD's reliance on the controversial tactic of stop-and-frisk, where officers routinely search large numbers of men in high-crime areas.

"We still have a number of trials to run before we can determine how best to deploy this technology, but we're very pleased with the progress we've made over the past year," Commissioner Kelly said.