Air travelers know well the standard technology of airport checkpoints: walk-through metal detectors, baggage X-ray machines and passenger-screening wands. But, depending on the airport, travelers often encounter something out of the ordinary: a puffer booth at Reagan Washington National, for example, or a shoe scanner at Orlando.
The Transportation Security Administration has spent years testing technology with the potential to improve security and offer greater convenience for travelers. In many cases, those devices are being assessed in the real world of airports.
The TSA has had mixed results in its drive to find faster, more-accurate machines. Here's a look at some of TSA's major efforts:
Advanced X-ray machines
*Status: Scheduled for wide deployment.
Advanced X-ray machines that take high-resolution photos of carry-on bags may eliminate the requirement that passengers take laptops out of their cases at security checkpoints. The TSA recently finished testing the machines at New York John F. Kennedy, Reagan Washington National, Los Angeles International and Albuquerque airports. It plans to install 250 in airports nationwide by next summer. They would replace conventional X-ray machines that have a limited ability to help security screeners find bombs.
Advanced X-ray has two important features: more vivid images of what's inside carry-on bags and the ability to photograph bags from two angles instead of one. It shows the images on side-by-side screens.
Both features give screeners a better picture of a bag's contents and could speed up security lines by reducing the number of times bags have to be put through X-ray machines a second time. The TSA says any changes in its policy requiring laptops to go through the X-ray machine separately would be in the distant future.
*Status: Being tested.
The TSA's most controversial technology, backscatter X-ray, has made a strong debut at Phoenix Sky Harbor International. The machines, which photograph travelers underneath their clothing to find hidden weapons, were held up for several years because of concerns that they produce vivid anatomical images.
The machine that launched at Phoenix in February has a privacy filter to produce blurred images that obscure details, but that screen reduces the ability to detect weapons. The TSA says it will begin testing backscatter machines at JFK and LAX but has not set a date.
The TSA uses backscatter machines in place of pat-downs on passengers who need additional checkpoint screening. They're too slow for initial screening in place of metal-detection gates. In Phoenix, such passengers are given a choice between a pat-down and a backscatter scan, and about 75% have chosen backscatter, the TSA says.
The machines emit small amounts of radiation, with each scan the equivalent to two minutes of the exposure from flying, according to federal research.
*Status: Tests scheduled.
The TSA will begin testing a related technology called millimeter-wave imaging at Phoenix in the near future, with additional machines to be tested at JFK and LAX. Millimeter wave operates on the same principle as backscatter, taking photographs of people under their clothing to find hidden weapons, although it uses non-radioactive electromagnetic waves to produce images. The machines to be tested will blur images of passengers.
The big advantage to millimeter wave is that the scans are fast enough to potentially use for primary screening in place of metal detectors. TSA Administrator Kip Hawley said the millimeter wave is being used at Amsterdam's Schiphol airport and "has a role in our future."
Handheld bottle scanners
*Status: Becoming increasingly common.
Handheld bottle scanners won't ease the restriction on the quantity of liquids and gels passengers can carry through checkpoints. But the $20,000 machines, in use at 19 airports, could improve security by checking bottles that hold medicine, baby formula and other items passengers can bring through checkpoints in unlimited quantities.
A sniffer on the machines is held an inch from a container to draw in vapors. An attached sensor displays the level of explosive material in the vapors and can detect explosives in glass, plastic and metal containers. The TSA plans to acquire 282 bottle scanners this year.
Bottle-scanning has been a priority since August 2006, when authorities disrupted an alleged plot to blow up U.S.-bound airplanes using liquid bombs. A subsequent policy that lets passengers carry only a half-dozen or so 3-ounce bottles through security is likely to remain in place for the near future.
*Status: Limited deployment.
One technology that has fallen short of expectations is trace portals, commonly known as "puffers." They shoot jets of air at passengers to dislodge explosives particles from clothing and skin. The portals, slightly larger than a phone booth, have built-in sensors to detect explosives residue.
The TSA had planned to install 434 of the machines, but the puffers have faced problems detecting explosives and from breaking down, according to a report this year by Congress' Government Accountability Office.
Only 95 machines have been installed at airport checkpoints. The TSA, which is working with manufacturers on improvements, has no plans to acquire more.
*Status: Sidelined for improvements.
Another checkpoint inconvenience -- shoe removal -- is likely to stay in place. Hawley last summer declared "not ready for prime time" a shoe-scanning device that was thought to hold imminent promise for use at checkpoints around the USA.
The ShoeScanner by General Electric subsidiary GE Security began operating with much fanfare in January at Orlando International.
Verified Identity Pass, a contractor the airport hired to run expedited security checkpoints for fee-paying passengers, installed the machine. Verified has installed ShoeScanners at airports in San Francisco, New York's Kennedy, Newark, Indianapolis, Cincinnati, Little Rock and San Jose, Calif. But the TSA won't allow the machines to be turned on because it says they are not good enough at finding shoe bombs or other weapons.
The machine is operating only in Orlando, where the TSA has added security measures to compensate for the ShoeScanners' deficiencies. An upgraded version of the ShoeScanner is being tested in a Homeland Security Department lab.