Low cost secure ID card and system

The invention provides a method for controlling the operating state of a lock characterized by a locked state and an unlocked state. The method comprises: entering secret information on an electronic input device (e.g. keypad) located on a radio frequency identity card, then electronically comparing the secret information against an authorized code to determine whether the secret information is authorized, then transmitting by radio frequency an unlocking signal to a radio frequency reader located at the lock for opening the lock in the event that the secret information is authorized. In a related use of such RF identity cards, the invention also provides a system and method of tracking movements of individuals within a secure area. The method comprises the steps of: using a loop antenna operable to transmit and receive RF signals from at least one radio frequency (RF) identity card carried by an individual; transmitting RF signals at a frequency not exceeding 1 megahertz from a reader through the loop antenna to the aforesaid RF card to request a secret code; entering this secret code on an electronic input device (e.g. keypad) device located on the RF card, transmitting this secret code to the reader through a transceiver disposed on the RF card; and using a data processor/CPU located at the reader to determine whether the secret code corresponds to the aforesaid authorization.