Originally Posted by
Wally Bird
Randomness is simple and I believe that at one time the TSA was doing it with the "continuous" secondary thing. You have a screener whose sole responsibility is to do these; the screener picks the next passenger in line, does the thing, then immediately picks the very next one and so on. Completely unpredictable and you can't "game" it because each secondary takes a slightly different amount of time.
Actually, you can still game the system a little bit, at selected moments. Suppose there's no-one in line at the WTMD. (It does happen ... smaller airports, out-of-the-way checkpoint, lull in the middle of the day, etc.). If I approach the checkpoint and see that the "continuous screener" is standing just past the WTMD, just waiting to select the next person through the WTMD for "random" screening, I know that I'm going to be randomly selected.
So ... I can game the system a bit. If another passenger approaches the checkpoint at about the same time, I can courteously allow them to go first --- say, by fumbling with my carry-ons, trying to figure out where I put my liquids bag, dropping stuff, etc.. Or, I can hang back from the checkpoint and wait until someone else goes ahead of me. At a minimum, I can wait until the checkpoint gets busy, to at least decrease the odds that I'll get picked.
There are numerous stories here about gate-screenings being conducted by TSA using the same "continuous screening" method ... and the amusing results when the gate agent calls for first-class boarding and no-one heads for the gate because they know the first person will be "randomly" selected for screening.
I'm just saying that "randomness" is a lot harder to achieve than you might think. This is one reason why casinos are so heavily regulated.