The Christmas Day airplane bombing attempt has renewed the debate over full body scanners at airports. The Transportation Security Administration in recent years has tried out a series of “whole-body imagers” to look for threats that typical metal detectors can’t find. These systems are the only way that smuggled explosives, like the one officials say was brought on the Christmas flight, can be reliably found [Wired.com].

Privacy advocates are calling the full body scanners a “digital strip search” (take a look at this TSA image of a full body scan and you’ll get the idea). But some security advocates say that either patting down every passenger or taking full body scans are the only options to ensure certain dangerous items are kept off airplanes.

Right now there are 40 full body scanners in 19 different U.S. airports. Only 6 airports use them for primary screening, the rest are used for follow-up searches. These scanners use millimeter-wave sensors that emit radio frequencies. By measuring the differences in the radiated energy, the scanner produces detailed 3-D images that resembles photo negatives. TSA has also ordered 150 similar scanners, at about $170,000 each, that use backscatter X-ray technology, after the completion of a successful pilot project.

TSA says privacy concerns are unwarranted since facial features (and other body parts?) are blurred out before the screening officer, who is in a separate room, sees the images. A senior U.S. air security source acknowledged the ongoing controversy over using the high-resolution body scanners that can show breast enhancements, body piercings and genitals. Full-body scanners currently in use in the U.S. have been set on a “politically correct” lower resolution that prevented screeners from seeing the outlines of genitals, the source said [New York Daily News]. Supposedly, the images will be permanently deleted immediately after screening.

Last June, the House of Representative voted 310 to 118 to oppose the use of full body scanners as a primary means of screening passengers. This doesn’t mean the issue is dead however, as President Obama has ordered a system-wide review on all screening procedures.

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Image: TSA