Security system to enable authenticated access of an individual to a protected area

摘要

A security system to enable access to a protected area, comprising a remote control unit (22) with a transponder (28), carried by an individual, which transmits an identification code on reception of an interrogation signal. A control unit, located within the protected area, transmits an interrogation signal when activated by the individual, and verifies the identification code received from the transponder. The transponder (28) obtains a supply voltage from the interrogation signal. The remote control unit (22) contains a battery (34) that can be connected to a supply voltage rail (46) by means of a controllable battery coupling switch (42) via a high-resistance path when the remote control unit (22) is in its quiescent state, or via a low-resistance path when the remote control (22) unit is in its active state. A pulse detector (58) obtains its supply voltage in the quiescent state via the high-resistance path. On reception of the interrogation signal by the transponder (28), the pulse detector (58) outputs a recognition signal. A remote-field detector (64) receives the recognition signal and outputs a remote-field signal as soon as the value of the recognition signal comes within a pre-determined range. A logic circuit (30), on reception of the remote-field signal, outputs a switching signal to the battery coupling switch (42) which switches this into the state where the battery (34) is connected to the supply voltage rail (46) via the low-resistance path; it then outputs an activation signal to the transponder (28) which will cause it to transmit the identification code. A near-field detector (66), on recognising a value of the supply voltage produced by the transponder (28) exceeding a pre-determined threshold value, outputs signal that causes the logic circuit (30) to put the battery coupling switch (42) into the state prevailing in the quiescent state, and to transmit the activation signal to the transponder (28).