Algorithm for RFID security

An exit control system is described that detects unauthorised removal of articles from a protected facility. A series of antennas are setup to produce interrogation corridors located near the exit of the protected area. RFID tags are attached to the articles to be protected. Each tag includes information that uniquely identifies the article to which it is affixed and status information as to whether the articles removal from the facility is authorized. When a plurality of tags are interrogated, the detection of a collision at status information bits is indicative of a non-authorized RFID tag.