The New York Police Department is working with the Department of Defense to develop a scanning device that would allow them to detect concealed firearms on a person 80 feet away. The scanner detects electromagnetic waves with a frequency in the terahertz range. Terahertz waves sit at the higher frequency end of infrared on the electromagnetic spectrum, just before the microwave range. The device works the same way an infrared detector does. Just as our bodies emit infrared radiation, so do they emit terahertz waves. These waves can pass through non-conducting material such as paper or clothing but are blocked by conducting material such as a piece of metal – or a gun. So if a person has a piece of metal under their jacket, such as a gun, the police will see the telltale outline of the weapon. The waves also pass unperturbed through wood and brick so the device can scan through walls.

The NYPD has a prototype that they’re testing at the department’s Rodman’s Neck shooting range in the Bronx. Right now, the prototype only has a range of three to five meters, but they hope to eventually be able to scan for weapons on people up to 25 meters, or 85 feet, away.

Of course, we can’t mention police and scanners and people without mentioning the ACLU. The New York Civil Liberties Union isn’t taking a hardline stance against the frisking from a distance. In a statement, the group acknowledged New York’s problem with gun violence and pointed out that using the scanner could decrease the city’s stop-and-frisk rate by a half-million people annually. They also caution that “the ability to walk down the street free from a virtual police pat-down is a matter of privacy.”

New York state’s handgun licensing regulations are among the strictest in the country. As a result, 90 percent of guns used in New York crimes are illegal and from out-of-state. Currently the method for sniffing out guns tucked into jackets and jeans is to stop the person and frisk them. According to the New York Civil Liberties Union, 88 percent of these stop-and-frisks carried out in the city turn up nothing. That’s a lot of inconvenienced, annoyed and embarrassed people. In 2011, however, the NYPD collected over 800 guns – including an AK-47 – through stop-and-frisk. If police were able to park a van on a street corner and scan the people as they walk by – exactly the scenario the NYPD has in mind – the amount of people being screened would obviously increase dramatically. But, as the NYCLU’s point indicates, not everyone’s going to take kindly to being frisked without even knowing it.

No doubt trying to allay these types of concerns, NYPD Commissioner Raymond Kelly said that the police department has been in discussions with their lawyers for the past three years and that they foresee no constitutional issues with the device, reported NBC New York.

Privacy rights aside, they’re going to have other problems if they stop too many people with concealed iPhones and Androids.