Lamphone: Passive Sound Recovery from a Desk Lamp's Light Bulb Vibrations

In this paper, we introduce "Lamphone," an optical sidechannel attack used to recover sound from desk lamp light bulbs; such lamps are commonly used in home offices, which became a primary work setting during the COVID-19 pandemic. We show how fluctuations in the air pressure on the surface of a light bulb, which occur in response to sound and cause the bulb to vibrate very slightly (a millidegree vibration), can be exploited by eavesdroppers to recover speech passively, externally, and using equipment that provides no indication regarding its application. We analyze a light bulb's response to sound via an electro-optical sensor and learn how to isolate the audio signal from the optical signal. We compare Lamphone to related methods presented in other studies and show that Lamphone can recover sound at high quality and lower volume levels that those methods. Finally, we show that eavesdroppers can apply Lamphone in order to recover speech at the sound level of a virtual meeting with fair intelligibility when the victim is sitting/working at a desk that contains a desk lamp with a light bulb from a distance of 35 meters.