A security system for facilitating transponder carrier identification and tracking within a secure area comprising an RF transponder having a memory in which is stored a unique identifier; the transponder including a transmitter to transmit the unique identifier; a transponder writer operable to send a replacement unique identifier to the transponder, the transponder replacing the identifier in the transponder memory with the replacement identifier; a transponder reader to receive from the transponder at least the unique identifier of the transponder; such that the transponder reader interrogates the transponder and, in response to the interrogation, receives from the transponder at least the unique identifier of the transponder; wherein the location of the transponder is determined from the location of the transponder reader.