Proximity Cardâ 125 Khz RFID Cards
Proximity cards, also known as prox cards, are low frequency 125 kHz credentials that feature an embedded metallic antenna coil that stores cardholder data. Data stored on a proximity card, key fob or tag can be detected by a reader when the proximity card is passed within range.
A proximity card or prox card is a "contactless" smart card which can be read without inserting it into a reader device, as required by earlier magnetic stripe cards such as credit cards and "contact" type smart cards. The proximity cards are part of the contactless card technologies. Held near an electronic reader for a moment they enable the identification of an encoded number. The reader usually produces a beep or other sound to indicate the card has been read. Proximity cards typically have a read range up to 50 cm (< 15 inches) which is the main difference with contactless smartcard with 2 to 10 cm (1 to 3 inches) . The card can often be left in a wallet or purse, and read by simply holding the wallet or purse near the reader. The term "proximity card" refers to the older 125 kHz devices as distinct to the newer 13.56 MHz contactless smart cards.
The card and the reader unit communicate with each other through 125 kHz radio frequency fields, (13.56 MHz for the contactless smartcard cards) by a process called resonant energy transfer. Passive cards have three components, sealed inside the plastic: an antenna consisting of a coil of wire, a capacitor, and an integrated circuit (IC), which contains the user's ID number in specific formats and no other data. The reader has its own antenna, which continuously transmits a short range radio frequency field.
When the card is placed within range of the reader, the antenna coil and capacitor, which form a tuned circuit, absorb and store energy from the field, resonating like an electrical version of a tuning fork. This energy is rectified to direct current which powers the integrated circuit. The chip sends its ID number or other data to the antenna coil, which transmits it by radio frequency signals back to the reader unit. The reader checks whether the ID number from the card is correct, and then performs whatever function it has been programmed to do. Since all the energy to power the card comes from the reader unit, passive cards must be close to the reader to function, and so have only a limited range.