Abstract: A coin fraud prevention system which includes a coin telephone having a voice transmitter, comprising a coin tone sensing arrangement for sensing coin tones, coupled to the voice transmitter of the telephone; and a coin telephone disabling arrangement in the coin telephone coupled to an output of the coin tone sensing arrangement for disabling the coin telephone in response to sensing of the coin tones from the transmitter; wherein further the coin tones include at least one or two coin tone frequencies, and the system has a bandpass filter having at least one pass band corresponding to the tone frequencies, and a tone detector coupled to the bandpass filter for generating a coin telephone disabling signal in response to receipt of the tone frequencies, wherein the disabling signal is connected to the coin telephone disabling arrangement, so as to prevent dialing of the call.

Abstract: A volume control for a telephone having a receiver, a manual key for generating a volume increment for each operation of the key; a volume increment counter connected to the manual key for counting volume increments; a controlled gain amplifier connected ahead of the receiver; and a gain control network connected between the controlled gain amplifier and the counter for controlling the gain of the amplifier in response to the number of volume increments counted in the volume increment counter. A unique feature of the volume control is that it maintains the selected gain level when the central office collects or refunds coins or makes an initial rate or coin present test.

Abstract: A pin fraud and shock prevention circuit for a pay telephone which has a receiver and transmitter, a tip and ring conductor forming a current loop connecting the pay telephone to a telephone exchange, and which has a current sensor in the ring conductor, a plurality of current switches coupled to the current sensor for connecting the receiver and transmitter to the loop in response to current flowing in the loop.