Airport officials on Friday showed off new X-ray scanning machines they will use to screen more passengers with full-body imaging as called for by security advocates, a step that has alarmed civil libertarians.
The USD$170,000 machines show images of passengers' bodies through their clothes to reveal hidden objects.
Three to be activated on Monday at Boston's Logan Airport will be the first of 150 the US Department of Homeland Security officials hope to deploy in the next few months using funds from last year's American Recovery and Reinvestment Act, also known as the stimulus.
The agency aims to have 450 advanced scanners at airports by the end of the year.
US congressional leaders called for more full-body imaging after a Nigerian man was charged with trying to blow up a US-bound airliner on Christmas Day using explosives smuggled onboard in his underwear.
DHS has asked for another USD$214.7 million to buy 500 more advanced scanners, which coupled with previous orders would place the imaging machines in most of the country's largest airports.
Officials in Boston, where two of the four airliners hijacked on September 11, 2001, took off, said they asked to be the first to receive the machines, which the agency will also deploy soon in Chicago and Los Angeles, among other cities.
For some randomly selected passengers they will replace the ubiquitous metal detectors. Passengers can choose a pat-down search instead, though in past tests nearly all preferred the imaging scanners, officials said.
Logan airport has previously tested another imaging machine made by L-3 Communications that analysed natural "millimetre wave" energy radiated by travellers' bodies.
The new machines, made by Rapiscan Systems, are known as "backscatter" machines and bounce low-energy X-rays off passengers.
Both machines create similar ghostly on-screen images of the flesh beneath clothing. In a demonstration for journalists using Transportation Security Administration workers as volunteers, however, software obscured the individuals' faces and groin areas to address privacy worries.
A cellphone one volunteer had concealed above her hip showed up clearly on the screen.
To win popular acceptance, TSA officials also set the machines to quickly discard the images rather than store them, and placed guards out of sight of passengers so they cannot tell who they are screening.
Groups including the American Civil Liberties Union are closely watching the rollout, citing worries over invasion of privacy for everyday travellers and raising concerns that images of naked celebrities could leak out to the public.
Travellers interviewed had mixed reactions at Logan airport. Sean Weston of Boston said he did not mind the machines, especially if the process used to pick passengers for screening is fair.
But his mother, Kathy Weston of Connecticut, was worried. "I think it's an invasion of your privacy," she said. Would the TSA's extra privacy measures ease her concerns? "None of it sounds delightful," she said.