A sensor for an electric fence barrier system comprising at least one electric fence wire is provided, the sensor comprising a mechanical sensing component to measure deflection of the electric fence wire to which the sensor has been fitted, and to produce a corresponding electrical deflection signal, an electrical activity monitoring component to measure the electrical activity on the electric fence wire to which the sensor has been fitted, and to produce an electrical activity signal, and a controller to receive and process the electrical deflection signal and the electrical activity signal, and to generate an alarm if either or both of the measured deflection or the electric activity exceeds predetermined values, and/or to communicate the electrical deflection and electrical activity signals to a remote location.
