Power line communication (PLC) networks are commonplace today, particularly within consumer home environments. They permit simple plug-and-play networking by leveraging the existing electrical wiring in buildings to transmit data as well as power. However, the ubiquity of this networking opportunity is often overlooked and permits an attacker, with only one-time access to an environment, to establish free, unmonitored and high-bandwidth network connectivity to the victim. However, the unsuitability of power wiring for high-frequency signalling means that PLC leaks radiated emissions. We demonstrate the detectability of this phenomenon in a real-world setting and introduce EMPower; a system that identifies the presence of hidden power line networking from analysis of the characteristic EM emissions in the frequency and time domains. We demonstrate the effectiveness of EMPower using a COTS radio receiver—identifying the presence of a network near-perfectly within the same room, even when idle, and with 74.6% accuracy two rooms away and on a different floor. Thus realising the capability to monitor an environment for unwanted power line networks.