Abstract: A system employing a plurality of electronic oscillators for generating test signals at spaced locations remote from a selection point. The oscillators are coupled to a gathering line for petroleum products, each being located adjacent to an acoustic detector coupled to the line for signaling the presence of a leak within its range. A digital selector which manually generates a given number of pulses is located at the selection point. There is a binary counter at each oscillator to receive the pulses. And, there is also a binary encoder at each oscillator to determine which one will be energized, depending upon the number of pulses generated by the selector.