A description is given of a system for monitoring the voltage at a remote location and determining when the voltage exceeds upper and lower levels. The system includes transmission lines for transmitting the voltage back to a central station and applying such to an amplifier having a pair of outputs. One of the outputs of the amplifier is applied to an oscillograph. The other output is fed through an isolation transformer, a full wave rectifier, to a pair of unijunctional transistor circuits for producing pulses when the voltage exceeds or drops below a predetermined level. These pulses, in turn, energize a relay which turns on the oscillograph for recording the voltages being monitored
