Shoes:

Walk-through magnetometers are consistently ineffective for detecting metal in shoes. Trying to conceal metal contraband, a passenger once shuffled his feet. This is the reason for the instruction to "walk thru at a normal pace (or gait.)"

Magnetometers must have their sensitivity set so as to disregard the metal building materials of modern concourse floors, which can also desensitize them to shoes, snaps and zippers.

During the random hand held metal detector search and the searches with cause, the common metal 'last' built into the sole of boots and sturdier shoes will activate the detector. Wearing running shoes or moccasins regularly forestalls extra searches.

There is no non-destructive way to inspect or test a passenger's shoe so as to differentiate between the metal last and contraband. Thus, sending shoes through the x-ray machine is the only reliable method of identifying possible hazards.