Last week, as noted on Reason 24/7, The New York City Police Department announced that it's rolling out portable terahertz scanners that will let police "see" if people on the street are carrying metal objects, like firearms. It'll give the cops yet one more reason to hassle people going about their business — a practice that's already raising judicial eyebrows. Of course, the scanners are premised on the idea that the items people carry are necessarily recognizable, but their very existence may create demand for versions of forbidden, suspicious or valuable goods that aren't so easy to spot.

As CNet described the new scanners:

The scanner is a device small enough to fit in a police van or set up on a street corner that reads terahertz radiation, which is energy emitted by both humans and inanimate objects. When aimed at a person, it's possible to see anything that is blocking the specific energy coming off the human -- such as a gun.

"If something is obstructing the flow of that radiation, for example a weapon, the device will highlight that object," Police Commissioner Raymond Kelly said, according to the New York Daily News.

Since anything metal will block the radiation, police will be looking for recognizable outlines. Specifically, they're assuming that a gun will look like a gun. That's traditionally been a safe assumption, since disguised weapons are generally categorized as Any Other Weapons under the National Firearms Act and subject to strict regulation. But guns that don't look like guns were a bit of a craze in 19th century America, and there's a market — usually illegal — for them elsewhere. Pen guns are old hat, and European headline writers worked themselves into a frenzy a decade ago when officials discovered that somebody in the Balkans was manufacturing four-shot .22 pistols that looked like cell phones.

With desktop manufacturing coming to a workshop near you, and eager activists already hard at work to circumvent gun controls, it's easy to imagine Defense Distributed, or somebody similar, creating downloadable plans for guns that don't look at all like guns, the better to befuddle the snoops in blue.

But gun-toters aren't the only people who might not be comfortable with the idea of law-enforcement officers lifting the veil, so to speak. Journalists have long had a ... strained relationship with the powers-that-be, and they may not want police so-easily identifying them by the cameras and recording equipment stuffed in their pockets. Neither would activists monitoring police behavior at a demonstration or during an arrest. Most of this gear has been miniaturized in recent years anyway. So why not anonymize it, too? Sunglasses that record video and audio have already been developed for the upload-my-skydive-to-Youtube set, so we're not far off.

Even people who usually consider themselves to have nothing to hide from the police may begin to feel uncomfortable revealing their possession of expensive watches or high-end electronics to public employees who aren't always on the up-and-up. Or, for that matter, public agencies seeking new applications for their toys. Why, of course, scanners would never be used to reveal the ownership of valuables that might contradict the claims made in a tax return.

Unless scanner-blocking metal-mesh clothing comes into wide vogue (limited use would just advertise a suspicious sense of modesty), we may soon live in a world in which  many items are designed to be unidentifiable.