Abstract: A low power consuming signal detection device for attachment to a telephone line. The device has an impedance of at least five megohms across the telephone lines. The device includes a power supply having an input impedance of least five megohms and an amplifier powered by the power supply for amplifying tone interrogation signals present on the telephone line. A phase-locked-loop is responsive to the amplifier signals for determining when the frequency of the amplified signals are within a predefined bandwidth. Phase locking of the phase-locked-loop to the amplified signals is detected by a lock detector when the frequency of the signals falls within a predetermined bandwidth for a predetermined period of time. the lock detection signal is used to place meter reading circuitry in an "off-hook" condition and for effecting the transfer of data from meter data collection apparatus over the telephone line back to a remote location.