Spying on digital conversations can be difficult – it usually requires a successful infiltration of a secured connection (a “man-in-the-middle” attack), compromising one of the involved devices, or planting recording equipment in the room that will have the conversation. Things like shotgun or laser microphones can let you pick up sound from a distance, but they can be defeated by white noise, such as running water, or poor atmospheric conditions (such as fog for laser mics).
Researchers have developed a novel way of extracting information – by monitoring micro-fluctuations in the status lights of electronic devices (such as a power light on a laptop), they are able to recreate the sounds created by the speakers of the device they are attached to. This is possible because how circuits operate is well-known and the minuscule variations in power used to create sound via the attached speakers. While this attack can be defeated by covering the status lights, hiding them from view may not be enough – researchers were able to extract some conversations from the status lights of other devices in the room.