Abstract: A switching device for a telecommunications channel. The device comprises a voltage detector, a switch, and a storage device. The voltage detector produces an output voltage if the voltage between the lines of the channel exceeds a predetermined level, for example 110 volts. The switch can increase an impedance in one of the lines (preferably causing open circuit) in response to an input voltage. The first storage device, for example a capacitor, produces the input voltage when it reaches a charge V.sub.2 ; is initially at a voltage V.sub.1, for example zero, that is less than V.sub.2 ; after charging by the output voltage from the voltage detector, is at a voltage V.sub.3 greater than V.sub.2 ; and discharges from V.sub.3 to V.sub.1 in the absence of the output voltage. The voltage detector comprising a low-pass filter such that an AC signal on the channel produces an output voltage that charges the first storage device to a charge below V.sub.2.