Device for locating audio surveillance apparatus

A device for use in conjunction with a detector of covert audio surveillance apparatus of the type which senses information in the audio frequency range and which includes a transmitter for generating electromagnetic signals comprising a carrier frequency modulated by said information, said detector demodulating the electromagnetic signals to develop separate output signals representative of the carrier frequency and said modulating information, said device including:

• means for producing discrete acoustic pulses and for propagating said pulses towards said transmitter portion;
• means responsive to an input signal for initiating a first timing interval of predetermined duration;
• means joined to said detector and to said timing interval initiating means for actuating said acoustic pulse producing means at the termination of said interval to produce and propagate a first acoustic pulse, said means preventing the actuation of the acoustic pulse producing means when an output signal representative of modulating information occurs during said interval;
• means responsive to the actuation of said pulse producing means to initiate a second timing interval of predetermined duration;
• means joined to said second timing interval initiating means and responsive to an output signal developed by the detector in response to receipt of modulating information during said second timing interval for actuating said acoustic pulse producing means to produce and propagate a second acoustic pulse;
• a first means for measuring the time interval occurring between the actuation of said pulse producing means which produces and propagates said first acoustic pulse and the development of an output signal by the detector in response to receipt of modulating information during the second time interval initiated by such actuation;
• a second means for measuring the time interval occurring between the actuation of said pulse producing means which produces and propagates said second acoustic pulse and the development of an output signal by the detector in response to receipt of modulating information during the second timing interval initiated by such further actuation;
• means for comparing the time intervals measured by said first and second measuring means;
• and
• means joined to said comparing means for providing an alarm when the measured time intervals are equal.