In the 1950s, young comic book readers were sold on advertisements for X-ray glasses, a novelty that did little more than provide an illusion which an adequately theatrical performer could exploit.

More than 50 years later, the security industry has developed their own version of X-ray vision -- one that actually works.

Using something called millimeter-wave technology and other cutting-edge tools, security professionals can literally see through clothes to spot anything that could be potentially dangerous.

But even in a world where many people fear being the victim of terrorism, does technology that can look under your undergarments cross the line?

Protecting Transit

The recent London terror attacks have prompted many to ask how we can effectively protect any transit system from terrorist attack.

"In this new sort of environment of security, the secret of success is constant vigilance -- being able to spot the anomaly in everyday life," said Neil Fisher, a vice president at QinetiQ, a British company that deals in defense technology and security solutions. "People are very bad at that, but technology is very good."

QinetiQ and other companies have been working with millimeter-wave technology for several years. Recently, they've started putting it in use in real-life situations.

QinetiQ's technology was used to scan soft-sided trucks and to look for people trying to illegally enter the United Kingdom at the country's ports. It's also been tried at airports in England, Europe and Canada. Fisher says his firm's machines have assisted in the apprehension of thousands of people trying to sneak through the French port of Calais.

Ready for Prime-Time?

Millimeter-wave technology takes advantage of harmless radiation commonly known as "cold light" that reflects off of humans and other objects when the sun's light strikes directly or indirectly.

"Our [QinetiQ] sensors are a bit like a camera in that it picks up reflections of this radiation on everyday objects," explained Fisher. "It just so happens that it reflects very well off metal, some plastics, some ceramics and organic material [like skin] and it doesn't reflect very well off clothing, which basically is transparent to it."

But millimeter-wave is not the only technology capable of taking a peek at what you may or may not be concealing under your clothes.

The Justice Department says there a number of other methods currently being researched to expose what terrorists or other criminals might want to conceal.

"We've got a technical partner at the Air Force Research Laboratory in Rome, N.Y., that is doing sort of a 'bake-off' of concealed weapons detection systems," said Dr. John Morgan, a Justice Department spokesman. "That includes some of the very best infrared systems along with some of these millimeter-wave systems."

Morgan believes that although millimeter-wave technology is promising, it's still not ready for the front lines.

"I would put them in the category of the 1960s mainframe computer," said Morgan. "If they can make them cheaper, smaller, faster, then they could have a real benefit to counterterrorism and law enforcement."

Privacy Concerns Persist

Anyone who's been to a U.S. airport since 9/11 has seen officials search passengers and their luggage.

But even at a time when air and even rail travelers are getting used to being scrutinized, is a machine that can see through your clothes a step over the line?

"I don't think it's a Big Brother thing," said Fisher. "I think with a system that can screen large amounts of people very, very quickly, who all they want to do is go about their daily business unhindered knowing that they're actually innocent, this technology isn't going to reveal anything."

Fisher says that the imaging is intentionally blurred and doesn't clearly show anything you wouldn't want the device's operator to see.

Despite progress in advanced ways to spot concealed dangers, Morgan admits technology alone is not going to do away with terror.

"Millimeter-wave is very good at raising the barrier, make it harder to do terrorism, to get someone at that last minute before they might do something terrible or tragic," Morgan said. "But it's only one piece of a very, very complicated puzzle."