System for preventing establishment of unauthorized communication

A system (17) that prevents unauthorized establishment of wireless bidirectional communication between a communication master (5) and a communication terminal (2). The system (17) includes a strength measurement signal transmission circuit (19) that transmits a received signal strength measurement signal (18), which is used to measure received signal strength at the communication terminal (2), a number of times with different transmission strengths during a single wireless bidirectional communication session. A received signal strength measurement circuit (23) measures the received signal strength of the received signal strength measurement signal (18) whenever the received signal strength measurement signal (18) is received by the communication terminal (2). A measurement result transmission circuit (24) transmits received signal strength measurement results as a single response signal (Srs) to the communication master (5) from the communication terminal (2) during the single communication session. A check circuit (26) checks whether the current bidirectional communication is authorized based on the received signal strength measurement results from the communication terminal (2).