Magnetometers, X-Rays, and More: Airport Security Technology

High-tech security scanners that might have prevented a would-be Christmas Day bomber from boarding a jetliner to the U.S. have been installed in only a small number of airports around the world, in large part because of concerns that the machines, which can "see" through clothing, invade the privacy of travelers.

But full-body imaging machines are just one of many types in use at airports around the country. Here are the five main technologies you'll find the next time you travel:

Magnetic imaging:
The strongest level of security being considered today relies upon passive millimeter wave (MWM) detection to create full body images of travelers. MMW scanners can see through clothing to reveal metallic and non-metallic objects or other suspicious things on a passenger's body, but they cannot identify explosives by their chemical signatures. The images they transmit are reviewed by security personnel who can't see an individual's face and don't know their identity, adding a level a privacy.

But unlike currently employed screening machines, which can identify banned chemicals directly, MMW scanners (also called "radiometric scanners") are only anomaly detectors. The body-scanning technology is in at least 19 U.S. airports, while European officials have generally limited it to test runs.

Jay Stanley, public education director for the American Civil Liberties Union's Technology and Liberty Program, has said that the machines essentially perform "virtual strip searches that see through your clothing and reveal the size and shape of your body." Body scanners cost between $150,000 and $200,000, according to Peter Kant, vice president of global affairs for Rapiscan Systems.

X-ray imaging:
The TSA has also invested in "backscatter" machines, which use low-level X-rays to create a two-dimensional image of the body, from Rapiscan Systems, a unit of OSI Systems Inc.

Within these scanners, the reflection or backscatter of a narrow, low energy X-ray beam off the body is detected, digitized and stored. The data is then enhanced to create a display of the person and any concealed objects. These machines, which cost $190,000 each, are expected to be deployed in U.S. airports in 2010. Baggage checking x-ray machines are less expensive, running between $35,000 and $45,000.

"The machine gives a very accurate and very precise image of things on the body that are not the body," Peter Kant. As with MWM scanners, backscatter machines penetrate only the surface of the skin, and cannot detect objects within the body.

Puffer machines:
In May, the TSA abandoned "puffer machines" that blow air onto passengers to dislodge trace amounts of explosives from the hair, body, clothing and shoes. Aided by gravity, these particles are then directed into the scanner for analysis. The machine can then look for trace amounts of explosives or drugs, through a process called ion mobility spectrometry (IMS). The scanner examines the weight of the various molecules from the body to look for those  specific substances.

The machines cost around $160,000 to purchase, although the government has said that they cost too much to maintain and regularly broke down when exposed to dirt or humidity. There are still 18 puffer machines deployed at U.S. airports, manufactured by made by General Electric Co. and Smiths Detection.

The metal detector is the most-used form of airport security. A magnetometer uses an electromagnetic field to detect metal objects, such as concealed handguns. The security devices can't detect ceramic or plastic weapons, however.

Magnetometers are relatively inexpensive devices, selling for just $10 to $15,000. While the procurement costs are less, they require more staff to run, and may be as expensive as full-body scanners in the long run. Explains Kant, "body imagers have lower operating costs and use fewer screeners, so you save in personnel costs."

Some airport security personnel use handheld trace detectors, in which an operator takes a swab of someone's hands and baggage to establish if he has been in contact with explosive material. The swab is then analyzed in a machine, either for bomb or explosive residue or for traces of drugs.

LiveScience and the Associated Press contributed to this report.