Does Kyllo v. United States Apply to A Scan of A Person? And What is the Standard for A “Terry Scan”?

New technologies often prompt new and interesting Fourth Amendment issues. Here’s the latest:

Get ready for scan-and-frisk.

The NYPD will soon deploy new technology allowing police to detect guns carried by criminals without using the typical pat-down procedure, Police Commissioner Raymond Kelly said Wednesday.

The department just received a machine that reads terahertz — the natural energy emitted by people and inanimate objects — and allows police to view concealed weapons from a distance.

“If something is obstructing the flow of that radiation, for example a weapon, the device will highlight that object,” Kelly said.

A video image aired at a Police Foundation breakfast Wednesday showed an officer, clad in a New York Jets jersey and jeans, with the shape of a hidden gun clearly visible under his clothing when viewed through the device.

The department will begin testing the high-tech device for use on the street. The device is small enough to be placed in a police vehicle or stationed at a street corner where gunplay has occurred in the past.

. . . [Kelly said:] “We still have a number of trials to run before we can determine how best to deploy this technology. We’re also talking to our legal staff about this. But we’re very pleased with the progress we’ve made over the past year.”

Use of this technology raises two primary Fourth Amendment questions. First, does it constitute a search under Kyllo v. United States? More specifically, does Kyllo apply when the device is used to obtain details from inside a person’s clothes rather than inside a home? And second, if use of the device is a “search” under Kyllo, what is the standard for when such a search is reasonable? Do you match the Fourth Amendment standard for a “virtual frisk” with the existing standard for a physical frisk? Or is the virtual frisk more or less invasive than the physical frisk in a way that would require more or less cause? Interesting questions. Thanks to Bruce Schneier for the link.

UPDATE: I should add that from the perspective of equilibrium-adjustment, a fair starting point would be to treat the virtual frisk just like they treat a physical frisk — allowing it and forbidding it in the same circumstances. Using the scanner would be a search that is reasonable only if there are specific and articulable facts to believe that the suspect is armed and dangerous. That way, the new technology does not considerably alter the preexisting balance of government power and individual rights.

The government’s counterargument presumably would be that scanning to detect a gun is less invasive than actually patting someone down to find a gun: Scanning is less obtrusive because it does not involve any physical invasion or retrieval. But Kyllo suggests that this sort of more or less intrusive analysis may not apply in the case of sense-enhancing devices. And given the fact that the scanning technology itself can change over time, it’s problematic to generate a constitutional rule that may only apply to the current version of the technology — assuming that it does for that.