Privacy-conscious travelers may cringe to think of the full-body scanners finding their way into dozens of airport checkpoints around the country. Most likely aren't aware that the same technology, capable of seeing through walls and clothes, has also been rolling out on U.S. streets.

American Science & Engineering  ( ASEI - news - people ), a company based in Billerica, Mass., has sold U.S. and foreign government agencies more than 500 backscatter X-ray scanners mounted in vans that can be driven past neighboring vehicles or cargo containers to snoop into their contents. And while the biggest buyer of AS&E's machines over the last seven years has been the Department of Defense for operations in Afghanistan and Iraq, the company says law enforcement agencies have also been using them domestically, deploying the roving scanners to search for vehicle-based roadside bombs in American cities. "This product is now the largest-selling cargo and vehicle inspection system ever," says Joseph Reiss, AS&E's vice president of marketing.

Good news, perhaps, for shareholders--and a nightmare for privacy advocates. "It's no surprise that governments and vendors are very enthusiastic about [the vans]," says Marc Rotenberg, executive director of Electronic Privacy Information Center (Epic). "But from a privacy perspective it's one of the most intrusive technologies conceivable."

Rotenberg sees the ZBVs as mobile versions of the same full-body scanning technique that has tested Americans' tolerance for intrusion as it's been deployed in airports around the country.

Though Reiss admits that the scanners "to a large degree will penetrate clothing," he points to the lack of features in images of humans like those above and on the previous page, pictures he says show far less detail than is captured in the airport scans. "From a privacy standpoint I'm hard-pressed to see what the concern or objection could be," he says.

Epic and others like the ACLU say a scan from a moving vehicle on a public road is even more likely to violate the Fourth Amendment than those used in the airport. "Without a warrant the government doesn't have a right to peer beneath your clothes," says Rotenberg.