In a 2006 opinion for the U.S. Court of Appeals for the 3rd Circuit, then-Judge Samuel Alito stressed that screening procedures must be both minimally intrusive and effective in other words, they must be well-tailored to protect personal privacy, and they must deliver on their promise of discovering serious threats. Alito upheld the practices at an airport checkpoint where passengers were first screened with walk-through magnetometers and then, if they set off an alarm, with hand-held wands. He wrote that airport searches are reasonable if they escalate in invasiveness only after a lower level of screening disclose a reason to conduct a more probing search. As currently used in U.S. airports, the new full-body scanners fail all of Alitos tests. . . .
U.S. courts have held that routine searches of all travelers can be conducted at airports as long as they dont threaten serious invasions of privacy. By contrast, non-routine searches, such as strip-searches or body-cavity searches, require some individualized suspicion that is, some cause to suspect a particular traveler of wrongdoing. Neither virtual strip-searches nor intrusive pat-downs should be considered routine, and therefore courts should rule that neither can be used for primary screening.
