Before a recent flight from Kauai, Arnold Villanueva was pulled aside for a security pat-down after the new full-body scanner at Lihue Airport detected an anomaly under his clothing.

The suspicious item? A couple of paper napkins tucked in his shorts pocket.

"Just because there’s a little wad of paper napkins, you gotta go through a full pat-down? Come on," said Villanueva, 54, of Ewa Beach.

Lihue Airport became last month the first airport in the state to begin screening passengers with the advanced imaging devices, which can look though a person’s clothing to produce full-body images. Other airports here are supposed to get them in the coming months.

Here and at airports nationwide, passengers are concerned about the new machines.

Many fear the technology allows security personnel to see them virtually naked – and that the images could fall into the wrong hands.

Others say the devices can produce false positives (as in Villanueva’s case) or that airport officials do not adequately inform passengers that they can opt out of the scanner – in which case they would go through an old-school metal detector and pat-down.

Either way, "Every single passenger is going to have some sort of invasive search," said Dan Gluck, senior staff attorney for the Hawaii chapter of the American Civil Liberties Union. "It’s a virtual strip search or a full pat-down of every single passenger."

Groups such as the ACLU, the Electronic Privacy Information Center, the Liberty Coalition and others are asking the Obama administration and Congress to suspend use of the new equipment until an independent review of privacy safeguards and any health effects.

The TSA said it has received about 600 complaints from passengers since the program began in 2007, mostly about invasion of privacy and failure to notify passengers of screening alternatives.

About 125 units have been installed nationwide so far.

"We expect 500 by the end of 2010, 1,100 by the end of 2011," said Suzanne Trevino, spokeswoman for the Transportation Security Administration. "This is definitely the next generation of airport screening."

The imagers use one of two technologies: backscatter, which uses low-level X-rays to produce images that look like chalk etchings; or millimeter wave, which uses electromagnetic waves to create vivid black-and-white images not unlike photo negatives. The Lihue scanner is a backscatter device.

"The amount of radiation from backscatter screening is equivalent to two minutes of flight on an airplane, and the energy projected by millimeter wave technology is 10,000 times less than a cell phone transmission," a TSA website says.

Trevino said passengers’ privacy is protected in several ways. The face of the subject is blurred; the security officer who sees the image never sees the actual passenger (and would radio a second officer if an anomaly showed up); and images are erased before the next passenger is scanned. The machine cannot store or transmit images, she said.

"Your image is gone forever," Trevino said.

Villanueva, a paramedic, said that had he known he could opt out of the body scan, "I wouldn’t have gone through" and instead chosen the metal detector and pat-down.

Two other passengers on that Kauai flight, Lily Smith and Tony Lalich of Waikiki, said they did not realize a full-body scanner had been installed at Lihue Airport.

In a passenger complaint to TSA – obtained by the Electronic Privacy Information Center through the Freedom of Information Act – a woman wrote she was not given a choice as to whether to go through the scanner.

"Given the choice, I would clearly have chosen the pat-down, as it is conducted by a person of the same gender. Instead, I was viewed through the whole-body imaging machine by a person of the opposite gender. This alone is perfectly unacceptable," said the woman, whose name was redacted by TSA. "I feel I was utterly violated."

In a May letter to the Electronic Privacy Information Center, TSA officials said the number of complaints is a small fraction of the millions of passengers scanned by the machines. TSA noted that a USA Today/Gallup poll found "78 percent of U.S. air travelers approve of the use of AIT (advanced imaging technology) screening in U.S. airports as a measure to prevent terrorists from smuggling explosives or other dangerous objects onto airplanes."

Since a failed bombing attempt aboard a Detroit-bound airliner last Christmas Day, the devices have detected more than 60 contraband items in passengers’ clothing at airports nationwide, TSA said. Items included illegal drugs and small knives, Trevino said.

"Our mission is to ensure that passengers are safe aboard an aircraft," Trevino said.

Gluck of the ACLU emphasizes the need to balance security concerns and passenger privacy.

"The government has an obligation to keep us safe but at the same time protect our civil liberties," he said.