A proximity card or prox card, also known as a key card or keycard, is a contactless card technology that can be read without being inserting into a reader device that was required by earlier developed contact type cards: magnetic stripe cards (credit cards, etc.). They are typically used as keycards for facilities access controls (doors, gates, etc.). In its simplest form, while being held near an electronic reader, they transmit a facility code (also called a "site code") and a card serial number Readers usually produce sound and/or show a status light to indicate the card has been held close for enough time to be read.
The term "proximity card" generally refers to the original 125 kHz devices without smart chips that do not hold more data than a magnetic stripe card and are distinct from devices that hold more data such as 13.56 MHz RFID and contactless smartcards or 900 MHz devices that can also be used for facilities access control when configured with a facility code and card serial number. Prox cards can be used for rough distance estimation applications. Passive prox cards typically have a longer read range of up to 50 cm (20 in) than a passive contactless smartcard’s range of 2 to 10 cm (1 to 4 in). The card can often be left in a wallet or purse, and read by simply holding the wallet or purse near the reader. Proximity cards with smart chips can hold other types of data like history of time and attendance or biometric templates.