Do you realize how pointless a metal detector at Wal-Mart would be? Virtually every customer would set the detector off. Just think about the number of completely mundane objects, which contain metals that most people have on their person on a daily basis... Keys, cellphone, belts, clothing (jackets, purses, etc), hats. That is not even taking into account how many people push shopping carts into and out of the store every minute. Or even how many products have metal in them (food packaging, electronics, toys, etc). It was probably just something malfunctioning..... You are worried about nothing.