A machine that senses the data encoded on a card and translates it into binary code that can be transmitted for further processing (see also magnetic card, smart card, punched card).

The magnetic card (or magnetic stripe) reader can have a power-driven transport that will draw the card into the machine and move it past the read head. The direction of travel is reversed after the card has been read and thus the card is returned to the user. In designs used with automatic cash dispensers the direction of travel may not reverse if the card and/or the associated identification number are not valid.

A slot reader is a relatively simple device for reading badges or plastic cards. The badge or card is manually moved along a slot that guides it past a sensing station. The data to be read may be encoded magnetically or printed in bar code or a machine-readable font. Since the rate of movement past the read head is not controlled by the device, the sensing head and electronics are generally designed to work over a range of speeds. Compared to a reader with a powered transport the device is much cheaper and quicker. Some designs for use with bank teller terminals can read the printed encoding on checks and the magnetic encoding on plastic cards.

The smart card reader has a guide and a connector that engages contacts on the card. When the machine senses that the card is in place and the related code has been keyed in, the memory device embedded in the card can be read. Some types can also modify the data on the card, e.g. debiting the amount of credit available.