Can someone explain what these traps are? "One of the investigators noticed that a set of steel shelves was on wheels. He yanked on them and they did not roll.

Can someone explain what these traps are? "One of the investigators noticed that a set of steel shelves was on wheels. He yanked on them and they did not roll. He then noted that they were held in place by magnets in the way of “traps,” the secret compartments used in cars to hide guns and drugs."