Radio-frequency identification (RFID) is a standard for identifying and keeping track of objects' physical locations through the use of radio waves. RFID has many different applications, but in the context of physical security, it is often used with identification badges. An RFID tag is attached to the badge and contains an antenna and a microchip. A lock containing an RFID reader continuously sends a signal into the area surrounding the reader. The RFID tag's antenna picks up this signal when in close proximity and the microchip generates a return signal. The RFID reader receives this signal and opens the lock if the signal is authenticated.
Unlike a card with a chip or magnetic stripe, an RFID badge does not need to be waved in front of the reader. It simply needs to be within a few feet of the reader, and can be inside of a bag, affixed to someone's shirt, or otherwise physically obstructed. RFID authentication systems can support granular access control with unique badges, allowing only certain badges to open certain locks. Although a badge is technically a "key" to the RFID lock, it helps to mitigate lock picking while still requiring that the user present a specific item for authentication.