Magnetic cards are used as passes, identity cards, to identify customers and members of clubs (spas, sports, etc.).
They are usually in the format of a plastic card with a magnetic tape on the back. This tape contains information about the owner of the card, which is read by the card reader.
After the operator swipes the card through the device, either the red indicator (not accepted) or green (accepted) lights up. The device itself is equipped with a magnetic head, which is used to read the code on the magnetic tape.