The document proposes a system to detect illegal electricity usage via power line communications (PLC). The system would add a secondary digital energy meter and PLC modem at the connection point between a subscriber's line and the main power lines. The recorded energy from this secondary meter would be compared to the value from the subscriber's primary meter. If a difference is detected, an error signal would be generated and transmitted over the PLC network, allowing detection of illegal usage. The proposed system architecture and components are described. Measurement results indicate the system could economically help reduce electricity theft.