As part of its ongoing effort to keep New York City safe, the NYPD has begun testing a new scanning device capable of detecting concealed firearms from a distance of about 16 feet. Developed in conjunction with the Department of Defense, the technology uses terahertz imaging detection to measure the radiation that humans naturally emit, and determine whether the flow of this radiation is impeded by a foreign object -- in this case, a gun. During a speech Tuesday, Police Commissioner Ray Kelly said the device shows "a great deal of promise as a way of detecting weapons without a physical search." Kelly went on to say that the technology would only be deployed under "reasonably suspicious circumstances," though some civil liberties activists are already expressing concerns. "We find this proposal both intriguing and worrisome," New York Civil Liberties Union executive director Donna Lieberman said in a statement, adding that the scanner could all too easily infringe upon civilian privacy. "If the NYPD is moving forward with this, the public needs more information about this technology, how it works and the dangers it presents." For now, the NYPD is only testing the device at a shooting range in the Bronx, and has yet to offer a timeline for its potential deployment.