Electronic security system with two-way communication between lock and key

Claim 1

A security system for controlling access through an entry point of an area or a system, said entry point having a locked state and one or more unlocked states, each said unlocked state allowing different access through said entry point, said system comprising: an access controller at said entry point, said access controller comprising: a memory storing a first code and one or more second codes; a first electromagnetic wave receiver for receiving electromagnetic energy modulated by codes and producing first signals containing the information in said codes in response thereto, first comparison means adapted to cause said security system to change from said locked state to one of said one or more unlocked states upon proper comparison of the information in codes contained in said first signals with the information in one of said one or more second codes, said one of said one or more unlocked states being a function of said second code that properly compares with the information in the codes contained in said first signals; and a first transmitter for transmitting an unmodulated activation signal followed by a signal modulated by said first code; and one or more electronic keys, each of said one or more electronic keys comprising: a memory storing said first code and a designated one of said second codes; a second electromagnetic energy receiver for receiving electromagnetic energy modulated by codes and producing second signals containing the information in said modulating codes in response thereto; second comparison means for comparing the information in portions of said modulating codes contained in said second signals and portions of said stored first code; a second transmitter for transmitting a signal modulated by said designated one of said one or more second codes upon the occurrence of proper comparison of the information in portions of modulating codes and portions of said stored code by said second comparison means; a source of electrical power; a power switch connected to said memory, said second electromagnetic energy receiver, said second comparison means, said second transmitter and said source of electrical power for selectively coupling electric power from said source of electric power to said memory, said second electromagnetic energy receiver, said second comparison means and said second transmitter; and a passive trigger receiver for receiving said unmodulated activation signal and triggering said power switch to supply electric power to said memory, said second electromagnetic energy receiver, said second comparison means and said second transmitter, upon receipt of said unmodulated activation signal, whereby each of said one or more electronic keys receives said unmodulated activation signal, switches on and transmits a signal modulated by its designated second code after receiving a signal modulated by the first code and properly comparing the information in a portion of the received first code with a portion of the stored first code, said access controller being operative to receive the signal transmitted by said one or more electronic keys, to compare the received designated second code with the stored one or more second codes, and to enter one of said one or more unlocked states upon the occurrence of a proper comparison of the received designated second code and one of the stored one or more second codes, said one of said one or more unlocked states being a function of said designated second code.