Security system for controlling building access

A security system for controlling access of a person through a controlled portal having a lock mechanism, comprising:

• a presence detector located near the portal which senses the presence of an object within an approach zone substantially adjacent the portal;
• a fixed transceiver located at the portal and electrically coupled to the presence detector, said transceiver being activated by said presence detector after an object has been detected in said zone by said detector, the fixed transceiver being adapted to generate and transmit an interrogation signal into said zone said interrogation signal further being receivable by a remote portable transceiver, the fixed transceiver further including a receiver capable of receiving a response signal from said remote portable transceiver in response to said transmitted interrogation signal, wherein the fixed transceiver automatically transmits the interrogation signal into the approach zone after an object is detected in said zone by the presence detector;
• said portable transceiver further being adapted to be carried by a person, and having a receiver capable of receiving the interrogation signal transmitted by said fixed transceiver and a transmitter capable of transmitting the response signal in response thereto, wherein the portable transceiver automatically transmits the response signal after receiving the interrogation signal;
• means for determining whether the response signal contains a valid access code;
• and
• means for unlocking the lock mechanism in response to receipt of a valid access code.