Abstract: The invention provides an electronic warning system, including an electrical line of a fence extending along a protected area; a pulser; a transmitter for transmitting pulses through the line; a receiver for receiving the pulses after being transmitted along at least a portion of the line; an impedance having a resistance substantially identical to the line characteristic resistance and connected at the end of the line, for absorbing the pulses when the pulses are received thereby at the end of the line so that the pulses do not return to the receiver; a plurality of sensors disposed at spaced-apart locations along the line and actuated responsive to phenomenon occurring in the vicinity thereof, for, when actuated, causing the pulses to return to the receiver; and a processor for operating the transmitter and receiver and for actuating a warning signal upon the detection, by at least one of the sensors, of the phenomenon.