Abstract: An electronic device for generating an activation signal in response to detection of an acoustic signal having parameters within respective predetermined ranges, and then automatically dialing a prestored telephone number and transmitting a prerecorded message over the telephone line in response to the activation signal. The device includes a transducer for transducing an acoustic signal into an electrical signal; a detector for outputting an activation signal in response to detection of an acoustic signal having parameters within respective predetermined ranges; and a telephone module for automatically dialing a prestored number and transmitting a prerecorded message in response to the activation signal. The detected parameters include the amplitude of the acoustic signal, the frequency of the acoustic signal, the duration of each burst of the acoustic signal, and the duration of each interval between successive bursts of the acoustic signal.

Abstract: A telephone transmission circuit for connection to telephone line terminals includes a transmitter amplifier, a receiver amplifier and a balancing circuit for suppressing the leakage of the output of the transmitter amplifier to the receiver amplifier, the transmitter amplifier being connected to the line terminals so that a power supplied from the line is effectively used. Good impedance matching between the line and the telephone transmission circuit is achieved by the automatic adjustment of the balancing circuit responsive to the line length between the telephone transmission circuit and an exchange.

Abstract: A telephone transmitter amplifier circuit is easy to manufacture in integrated circuit form and has a low power consumption. It has a microphone unit, and an operational amplifier including a differential amplifer. A grounded collector transistor is connected to the output of the differential amplifier and a constant-current circuit is connected to the emitter of that transistor. An output stage amplifier has a grounded emitter transistor having its base connected directly to the output terminal of the operational amplifier. A smoothing circuit smooths the voltage which is supplied from the telephone line to the amplifier. A voltage-divider circuit, at the output of the smoothing circuit, presets the operating points of the operational amplifier and the output stage amplifier. The output terminals of the output stage amplifier are connected in common to input terminals of the smoothing circuit.