Homeland Security Secretary Janet Napolitano on Monday vehemently defended her department's use of advanced imaging technologies and pat-downs at U.S. airports, saying to do otherwise would be "irresponsible" and that passengers who don't like it can "travel by some other means."

The metal detectors that "everybody's used to" went into place in the 1960s, and, "It would be unwise to say the least ... not to evolve our technology to match the changing threat environment that we inhabit," she said.

This comes two days after a California wan was forced to leave San Diego's airport for refusing to let security officers use full-body imaging or pat him down, telling them, "If you touch my junk, I'll have you arrested." At the same time, critics have launched an "opt out" campaign online, calling on those traveling the day before Thanksgiving to refuse full-body imaging, which would force Transportation Security Administration agents across the country to give pat-downs and, critics say, would let Americans "see for themselves how the TSA treats law-abiding citizens."

"The government should not have the ability to virtually strip search anyone it wants without cause," says the website OptOutDay.com. "We do not believe the government has a right to see you naked or aggressively touch you just because you bought an airline ticket."

Napolitano, however, said she "really regrets" such calls for an "Opt Out Day," insisting such full-body scanners "in no way resemble electronic strip searches" and travelers should "be realistic and use our common sense."

"This is just the next generation of travel security," she told reporters during a press conference at Ronald Reagan National Airport outside Washington. She said authorities have looked closely at "how can we best protect security and protect privacy, and keep those passenger lines moving -- all of which are values that have been expressed to us by the traveling public."

Specifically, she said, people scanned by imaging technologies with no "pings" are "done" in "about the same" time as those who go through metal detectors. Their images are only seen "in a private area, away from the gate," and those images are "neither retained nor transmitted," Napolitano said. But, if there is "a ping," that "tells an officer where they need to search," and such officers are "really the last line of protection we have for the aircraft," according to Napolitano.

"We built privacy screens into the machines, we built privacy concerns into the procedures when they were deployed," she said. "The [advanced imaging] machines have been in development for quite a long time, since before [the failed Christmas Day attack] . All we have done now is to accelerate their deployment. Why did we do that? Because our evaluation of the intelligence and risk indicated that we needed to move more quickly into the non-metal environment, to get [potentially dangerous] liquids and powders and gels off of aircraft."

Those who "refuse" advanced imaging machines "can go to a separate area for a same-gender pat-down, which is conducted as a law enforcement pat-down should be, in a very professional way," according to Napolitano.

Critics of the latest procedures, though, have been vocal, and online video of the California man's encounter at San Diego International Airport has been viewed by hundreds of thousands. 31-year-old John Tyner recorded much of the incident on his cell phone.

When he arrived at the airport early Saturday morning, Tyner had already read extensively about full-body imaging machines and "the possible harm to health as well as the vivid pictures they create of people's naked bodies," according to a posting on his blog. So when TSA agents directed him to one such machine, Tyner refused, prompting one TSA agent to tell him he would have to undergo a pat-down.

"After he described the pat down, I realized that he intended to touch my groin," Tyner wrote on his blog within hours of the incident. "Before he started the pat down, I looked him straight in the eye and said, 'If you touch my junk, I'll have you arrested.'"

When another TSA employee intervened, "I stated that I would not allow myself to be subject to a molestation as a condition of getting on my flight," according to Tyner, who said he feels the government took away his rights after the attacks of Sept. 11, 2001.

Authorities subsequently told Tyner he couldn't leave the airport without completing the screening because he "may have an incendiary device and whether or not that was true needed to be determined," Tyner wrote on his blog. And, authorities told him, he could face a civil lawsuit and a $10,000 if he left before the screening was completed, according to Tyner.

As for "Opt Out Day," organizers say many Americans "only fly around the holidays and may not be aware of the security changes."

"Once people are made aware of what is happening, they may have reservations about the new virtual strip searches and enhanced pat downs - especially for their children or spouse or other loved one," OptOutDay.com says. "This country needs security measures in place that not only keep us safe but also do not grossly violate privacy or constitute an unreasonable search, like the current protocol."

On Monday, Napolitano said TSA and her department are acting responsibly "with good intelligence, with risk-based analysis," and with partners around the world, but DHS can't be the only ones working to protect citizens.

"Look, everybody has a role to play," she said. "And if people don't want to play that role, if they want to travel by some other means, of course that's their right. This is the United States, of course they have that right. But again, this is all being done as a process to make sure that the traveling public is safe."

She said efforts by websites like OptOutDay.com amount to saying, "Well, we don't want to be a part of that. We don't want to play a part of security."

Napolitano was joined at Reagan National Airport by TSA Administrator John Pistole and other top law enforcement officials as they announced expansion of the "See Something, Say Something" campaign, which urges travelers to notify authorities of any suspicious activity they may see.

"Look, we know the threats are real," said Pistole, who spent more than 27 years at the FBI before joining Napolitano's department as head of TSA. "Whether it's 19 individuals with box cutters, an individual with a shoe bomb, whether it's individuals with explosives in liquids, whether it's an individual with explosives in his underwear, or cargo threats, we know that the threats are real. So what steps can we prudently take to make sure that the traveling public is safe?"

Asked about concerns over exposure to radiation from advanced imaging technologies, Napolitano said such concerns are unfounded, insisting the effects of full-body imaging machines "have been examined six ways to Sunday" by the entities such as the U.S. Food and Drug Administration, Johns Hopkins University and the U.S. Science and Standards Association. They found that the radiation involved is "almost immeasurable, it is so small," she said, adding that the exposure is equivalent to "about two minutes worth of being" on a plane, where passengers are routinely exposed to "miniscule" amounts of radiation.

Nevertheless, Napolitano said, if "adjustments" to the latest procedures need to be made, "We have an open ear, we will listen."