Abstract: A fault locating device for determining whether a problem exists on the customer side or the office side of a telephone line. A voltage and current sensitive switch is connected in series with each of the ring and tip lines near the customer side. The voltage and current sensitive switches are activated by a current demand only in the presence of a threshold voltage across the telephone line. The switches include a triac connected in series with each telephone line and a bilateral avalanche device connected to the gate of the triac and the telephone line. The switches will not turn on, and the customer will remain disconnected from the central office if the voltage is below the breakover voltage of the avalanche device. A distinctive termination circuit is connected across the tip and ring lines on the customer side of the voltage and current sensitive switches. The termination circuit conducts only when the ring is positive and the tip is negative.