Historically, card based access control systems were built around a card with a magnetic stripe. These cards required a swipe action through a magnetic card reader to gain access to a door. This technology had a number of disadvantages, including an inconvenience factor, a high wear rate, and very low security. It was these disadvantages that led to the development of a new contactless proximity technology, allowing cards to be read without physically contacting the reader.
Proximity readers work by constantly emitting a short range RF field. When a proximity card comes within range of this field, an integrated chip within the card is powered up and the chip transmits a card number back to the reader. Not all proximity cards are born equal however, and it is important that the differences are weighed up before making a decision about which technology to adopt.