The invention (and I've actually seen these at Dulles as well) is a box with a metal detector in it that is used to pre-scan people's shoes. The trick is that most people don't know if their shoes are going to trigger the metal detectors or not these days. However, if they unexpectedly do, the whole line is in for a stop while the shoes are removed, the individual is hand-wanded, the shoes are sent through the x-ray machine, etc.
The box will beep if your shoes are going to impede the flow of traffic and annoy your neighbors, so you know to take them off.
Sounds like a good opportunity for a merit badge.