Cameras that could spot suicide bombers carrying bombs strapped to their bodies will be used in a new test aimed at securing the nation's rail and bus stations.
The Transportation Security Administration says it is the first agency to use heat-sensing cameras that spot objects hidden under people's clothing. The small, portable cameras can be positioned anywhere — at an entrance to a transit station or a building — and can screen people without having to require them to go through time-consuming checkpoints.
Some of the deadliest recent terrorist attacks have involved mass transit, including the 2004 Madrid train bombing that killed 191 people and the 2005 London subway and bus attacks that killed 52.
But the technology also could result in innocent people being searched if the machines flag benign objects such as wallets and cellphones, say experts and privacy advocates such as the American Civil Liberties Union.
The machines screen people one at a time by taking a quick thermal image of their body. A camera highlights "cold" objects such as metals, plastics and ceramics, but does not identify the material. Objects that are a certain minimum size and in certain locations will trigger a red light on a computer monitor, prompting a screener to search the person, the TSA said.
"This gives us additional screening capabilities in a mass-transit environment without stopping the flow," TSA spokeswoman Amy Kudwa said. The machines, weighing about 45 pounds with a 10-inch camera, can be moved easily.
Manufacturer QinetiQ North America hopes to see the technology used at military bases, landmark buildings, large events, arenas and possibly stores trying to catch shoplifters, said Wally Miller, the company's managing director for transportation security.
Because the machines can screen someone from 20 yards away, they could detect a suicide bomber before he reaches his target.
"It's clearly something the military would want," Miller said.
Barry Steinhardt, head of the ACLU's technology program, said the machines' value is unproven. "Lots of things look like guns or explosives. It's going to result in people being needlessly searched or worse," he said.
The cameras, which use millimeter-wave technology, won't store images of people or display anatomical details, the TSA's Kudwa said. "People can be scanned without interfering with them in any way," she said.
The TSA bought 12 machines from QinetiQ for $3 million to test in labs and transit stations in the next eight months.
Erich Grossman, a physicist with the National Institute of Standards and Technology in Colorado, said the technology shows promise for use in mass transit but needs to improve its ability to screen large numbers of people quickly.
"There are still some unanswered questions about how well it can reject false positives and detect true threats," said Grossman, who is researching the technology. The machines can be programmed to detect more suspicious — and benign — objects.
"There's no question in my mind that this will at some point be deemed not only useful but essential," Grossman said. "It's just a matter of time."