SAFETY FIRST? These scanners DO NOT WORK! They work between microwave and infrared frequencies to detect body heat and any objects in between will hide the infrared heat from the body and show as dark areas on the monitor.
The video from Germany, Nacktscanner with Mark Lanz (finally with English subtitles), shows how the scanners can easily be fooled.
[Youtube] The Humorous Full Body Scanner
[Youtube] Full Body Scanner easily fooled