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[s] a reason to conduct a more probing search.”

As currently used in U.S. airports, the new full-body scanners fail all of Alito’s tests. First, as European regulators have recognized, they could be much less intrusive without sacrificing effectiveness. For example, Amsterdam’s Schiphol Airport, the European airport that employs body-scanning machines most extensively, has incorporated crucial privacy and safety protections. Rejecting the “backscatter” machines used in the United States, which produce revealing images of the body and have raised concerns about radiation, the Dutch use scanners known as ProVision ATD, which employ radio waves with far lower frequencies than those used in common hand-held devices. If the software detects contraband or suspicious material under a passenger’s clothing, it projects an outline of that area of the body onto a gender-neutral, blob-like human image, instead of generating a virtually naked image of the passenger. The passenger can then be taken aside for secondary screening.