When I was screening we had to randomly wand a certain percentage of the non-beeping passengers. To get less of a hassle from the non-beepers who I selected I would have them come through, quickly check their "star" count to make sure they were non-beepers and then place my shoe near the WTMD. I had steel-toed shoes so it would go off if my shoe was within a couple inches. Saved me grief although I'm sure I confused some people who thought they were clean. Not the most professional way to operate.