Magnetic stripe card readers read the data from cards with magnetic strips on the back (or front) - like your credit card (soon to be completely replaced by smart card technology). However, in access control, where speed of throughput is often important, the swipe card systems will typically use magnetic stripe readers, as they are slightly harder to copy than cards that contain barcodes. Bar code slot readers, that read cards with barcodes on, are more reliable, as they do not suffer from the effects of magnetic inteference and magnetic field decay.