The phenomenology of electrical signatures being unintentionally injected onto the mains electricity supply by a range of common household devices is investigated. Measurements were made of both current time series and voltage spectra of a variety of devices, using commercially available measurement equipment designed for electromagnetic compatibility testing. The measurements give strong evidence that multiple devices can be identified from either their current transient when switched on or off, or their voltage spectrum when running. While some devices are readily identifiable, even in the presence of large amounts of noise, for low power devices it may be necessary to perform filtering of the mains signal to obtain spectra with a suitable signal-to-noise ratio. For certain types of device, spectral signatures of particular instances of the same device appear to be separable in high signal-to-noise ratio environments. For example, it may be possible to identify a specific laptop charger among other chargers of the same make and model. The relevant measurements can be made outside buildings, and when combined with other intelligence, could be used to obtain remote intelligence of building interiors.
