a card with a magnetic stripe when fed into a card reader can be illegally read by a read head unobtrusively attached to the outside of the card reader adjacent to the slot into which the card is fed . to defeat this illegal reading , movement of a card through the read head is interrupted thereby making it difficult for the illegal read head to read the stripe . this interruption occurs at the point where the proper read head inside the card reader is not reading the magnetic stripe . the interruption can be a brief stop or a brief reversal in direction . the interruption occurs once while the card is being fed into the card reader and once when the card is being fed out of the card reader .