Proximity readers exist as part of a large access control system. Many organizations have their readers fitted to doors. From where they are, the readers emit electromagnetic field that experts call the excite field. This field is large enough and covers a large radius around the card reader.
The card absorbs some of the field’s energy and convert it to electricity. That way, the card’s circuit turns on so the card can transmit its numbers to the card reader.
The Proximity readers transmits the numbers from the card to the control system. The card has wireless communication with the reader, the reader has wires to send data to and from the system.