SIGNAL DETECTER

PURPOSE:To reduce unnecessary telephone line closing time, by performing remote control with the voice of a caller, even during the reproduction of response message or business message. CONSTITUTION:A remote control signal of voice or the like from a telephone line is detected, by comparing the zero crossing waves of response message or business message voice from zero crossing wave circuits 12 and 13 with that of a signal superimposed with the response or business message voice on a remote control signal such as voice from the telephone line at a comparison circuit 16 through the count at count circuits 14 and 15 for a prescribed time. Since the signals are converted into the zero crossing waves, the fluctuation of the amplitude, i.e., the effect of impedance of a public telephone line can not be affected. Further, since the difference of counts in an arbitrary time interval of the zero crossing waves is detected, the circuit can withstand sudden noise.