A method and apparatus for detecting signals transmitted via a power line to a node which have a source address portion equal to the predetermined address of an electrical metering device, but which were not transmitted by the metering device. Each electrical metering device of a power line communications system has a predetermined address and may monitor the source address portions of signals transmitted via the power lines. The electrical metering device thus detects or flags a power line signal if the source address portion of the transmitted signal matches the predetermined address of the electrical metering device. The electrical metering device may also count the signals having source address portions which match the predetermined address of the electrical metering device. Alternatively, the electrical metering device may transmit a predetermined message on the power lines if a signal is transmitted which has a source address portion which matches the predetermined address of the electrical metering device.