A security camera that can peer discreetly through clothing to spot explosives, drugs, and weapons will be shown at a government security conference in the United Kingdom on Wednesday.

Its maker, ThruVision Ltd., insists it can detect both metallic and nonmetallic objects under clothing without revealing details of the subject's body. The camera works at a range of up to 25 meters, making it potentially useful for both single-person screening and crowd scenarios.

Concerns about the personal privacy and dignity of travelers remain a point of contention for critics of high-tech scanning technologies. When the U.S. Transportation Safety Administration (TSA) last year began testing a millimeter wave scanning system at Phoenix Sky Harbor Airport last year, privacy and civil liberties groups expressed concern that the clothing-penetrating scans showed travelers' bodies in graphic detail and that such scans might not be optional in the future.

The TSA has dismissed worries about its technology, noting last year that in test of backscatter scanning -- a similar technology -- in Phoenix, about 79% of travelers singled out for secondary screening opted for a backscatter scan rather than a pat-down.

However, a 2007 report issued the National Research Council's Committee on Assessment of Security Technologies for Transportation concluded that "Millimeter-wavelength/terahertz image quality raises personal privacy issues that need to be addressed."

The ThruVision T5000 camera comes from space technology developed to scrutinize dying stars. It operates in the terahertz range of the electromagnetic spectrum, which typically includes frequencies from 300 GHz to 3 THz. Millimeter waves, the kind used by the TSA's scanner, fall within the 30 GHz to 300 GHz range.

Terahertz rays, or T-rays, remain a subject of interest to researchers because they can penetrate organic materials without the potential damage done by ionizing radiation like X-rays. Because T-rays are absorbed by water, they can be used to identify materials with differing water content, which is important in biomedical imaging; they can also be used to identify liquid explosives, which have become an issue in security screening.

"Acts of terrorism have shaken the world in recent years and security precautions have been tightened globally," said Clive Beattie, ThruVision's CEO, in a statement. "The T5000 dramatically extends the security surveillance envelope for ThruVision's passive body scanning products used at important sites and events. The ability to see both metallic and nonmetallic items on people out to 25 meters is certainly a key capability that will enhance any comprehensive security system deployment."

National Research Council's report sees promise in millimeter-wave and terahertz scanning technology but cautions that the TSA should weigh system cost, the probability of detection, the false-alarm rate, and the rate at which travelers can be screened against what's currently possible with X-ray systems.