Skydiverdriver,
A couple of posts ago, you mentioned that it would not be acceptable to subject ourselves to random auto searches even though driving was a privilege. Interesting point.
Some communities, in an effort to thwart drug trafficking, set up highway stops to conduct 100% or random searches. These were deemed illegal in original or appellate courts. The tactic governments have used to get around this is to identify a compellling reason for the original stop. Some use "safety checks". If during the course of a safety check, a whiff of marijuana was smelled (or any number of trigger events), then the officers had probable cause to search. We recently had what I thought was an extreme stretch of this principle used when a driver was arrested because, seeing the check point and not wanting to be delayed thusly, turned around and drove away.
Now as to how this policy could be applied to the subject at hand, I am not certain. Is walking through a metal detector with no probable cause an illegal search? If setting off a metal detector, is a wand an illegal search? If setting off a wand, is a manual search intrusive and illegal? Is turning away from the metal detector (change of mind from going by air) probable cause?