PURPOSE: A visitor-monitoring device based upon a non-contacting type ID card system is provided to prevent unauthorized visitor from entering the door which is not completely closed right after the entrance of the authorized visitor. CONSTITUTION: A visitor-monitoring device based upon a non-contacting ID type card system includes an RF receiver (12), a central processing unit (CPU) (14), a door lock controller (16) and an electric door lock (18). In addition, the visitor-monitoring device comprises an authorized visitor sensor (20) and an alarm unit (28) in order to generate an alarm signal and go off a siren. The RF receiver (12) receives radio frequency data from a RF card (10), and the CPU analyzes the RF data as well as checks the entrance permission of visitor. The electric door lock (16) controls opening and closing a door, and the door lock controller (16) controls the electric door lock under the control of the CPU (14). The unauthorized visitor sensor (20) includes an infrared sensor (22), a RF data detector (24) and a signal sensor (26). The infrared sensor (22) installed at entrance generates an entrance detection signal (A) after sensing a visitor, and the RF detector (24) receives a signal from the RF card (10) and then generates a radio reception signal (B). The signal processor (26) receives both the entrance detection signal (A) and the radio reception signal (B), and generates an alarm signal (D) when the entrance detection signal (A) is generated in the case of that the radio reception signal (B) is not generated.
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