Documents obtained Tuesday by the Electronic Privacy Information Center suggest that the U.S. Department of Homeland Security has signed contracts for the development of mobile and static systems that can be used scan pedestrians and people at rail and bus stations and special event venues -- apparently at times without their knowledge.

The documents indicate that DHS moved to develop the technology as part of an effort to bolster the ability of law enforcement personnel to quickly detect concealed bombs and other explosives on individuals.

EPIC obtained the documents from the DHS under a Freedom of Information Act request for data on mobile and static scanning systems it filed last year.

The documents show that the agency in recent years has signed contracts worth millions of dollars for the development of the new scanning technologies, said Ginger McCall, assistant director of EPIC's open government program.

For example, DHS contracted with Siemens Corporate Research and Northeastern University to design and develop an Intelligent Pedestrian Surveillance platform that could detect improvised explosive devices concealed in backpacks and under clothing.

The system would use multiple cameras mounted on a so-called Z Backscatter Van to covertly scan moving pedestrians for potential threats, McCall said. A Z Backscatter Van is a mobile threat detection system that uses X-Rays to quickly scan through vehicles and buildings for hidden explosives and contraband.

Another contract calls for Rapiscan Systems to develop a walk-through x-ray screening system that could be deployed at entrances to special events or other points of interest. The contract calls for a scanning system that could be installed in corridors and likely scan people walking through it without them knowing it, McCall said.

Among the tools mentioned in the DHS documents is an X-Ray Backscatter system that could detect concealed metallic and high-density plastic objects on people from up to 10 meters away.

The language used in many of the documents suggests that the DHS plans to use the scanners mostly in a covert fashion, McCall said. "The DHS believes it has very wide authority to implement its national security goals," she added.

It's unclear whether the projects have been completed, she said.

McCall contended that the use of such technologies to scan individuals without notice would be an invasion of privacy and a violation of Fourth Amendment prohibitions against unreasonable search.

In addition, the use of such technologies also raises several questions about the potential radiation risks that people could be exposed to, she said.

"In fact, the radiation risk is discussed several times in these documents," she said.

The DHS did not immediately respond to a request for comment.

In 2006, the DHS conducted a Rail Security Pilot project at the Port Authority Trans Hudson Exchange Place station in New Jersey to test the viability of using different types of body scanner technologies to detect concealed explosives.

Apart from that test, there has been no public word that the DHS has conducted similar tests at public transit locations, McCall said.

Jaikumar Vijayan covers data security and privacy issues, financial services security and e-voting for Computerworld. Follow Jaikumar on Twitter at @jaivijayan, or subscribe to Jaikumar's RSS feed . His e-mail address is jvijayan@computerworld.com.