An intrusion detection system disclosed herein includes a detector circuit that measures a change in value of impedance of an interconnection circuitry. A decoder coupled to the detector decodes the measured value of the change in the impedance of the interconnection circuitry to determine existence of an abnormal condition. In an example implementation of the intrusion detection system, the change in the value of the impedance of the interconnection circuitry is represented by a change in the phase delay on the interconnection circuitry. An implementation of the intrusion detection circuit terminates communication using the interconnection circuitry upon detection of the abnormal condition. The intrusion detection system is further configured to interpret the abnormal condition as a communication signal to the interconnection circuitry.