The New York Police Department already has the long arm of the law. Now it gets X-ray eyes. NYPD Commissioner Ray Kelly says 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. The boxy machine can be hidden in a vehicle, allowing officers to discreetly scan their target. “We still have a number of trials to run before we can determine how best to deploy this technology,” he said.