Abstract: A telephone test instrument permits voice communications with and monitoring of a telephone circuit to be tested. The instrument includes a microprocessor used in controlling various functions of the instrument. The microprocessor and other circuits of the instrument are energized from a connected telephone circuit and/or an internal energy supply which is automatically recharged from the telephone circuit. The microprocessor continually checks the voltage of the internal energy supply and automatically turns off a loudspeaker of the instrument, or prevents it from being turned on, if the voltage is too low. The instrument includes circuitry which, in combination with the microprocessor, measures loop current or line voltage while the instrument is connected for making voice communications with the telephone circuit. When the loudspeaker within the instrument is energized, the earpiece receiver remains active.