Contactless sensing of appliance state transitions through variations in electromagnetic fields


Non-Intrusive Load Monitoring (NILM) is a promising technique for disaggregating per-appliance energy consumption in buildings from aggregate voltage/current measurements. One major limitation of the approach is that it typically requires a training phase during which users must manually label device transitions. In this paper, we present an inexpensive contactless electromagnetic field (EMF) event-detector that can detect appliance state changes within close proximity based on magnetic and electric field fluctuations. Each detector wirelessly transmits state changes to a circuit-panel energy meter, which can then be used to label and disambiguate appliance transitions detected from the aggregate signals as well as to track the associated energy consumption. Our EMF sensors are able to detect significant power state changes from a few inches away making it possible to externally monitor in-wall wiring to devices (e.g., overhead lights). We experimentally evaluate our proposed EMF sensor in terms of power consumption, accuracy and detection range on a variety of appliances to demonstrate its effectiveness towards augmenting NILM systems. We show that accurately detecting 100W loads from 10cm away is possible while maintaining multiple-year battery life from a coin-cell battery.