The Cyber@BGU team—consisting of Ben Nassi, Yaron Pirutin, Tomer Gator, Boris Zadov, and Professor Yuval Elovici—analyzed a broad array of widely used consumer devices including smart speakers, simple PC speakers, and USB hubs. The team found that the devices' power indicator LEDs were generally influenced perceptibly by audio signals fed through the attached speakers.
Although the fluctuations in LED signal strength generally aren't perceptible to the naked eye, they're strong enough to be read with a photodiode coupled to a simple optical telescope... more
Check out the other eavesdropping hits that have come out of Ben-Gurion University... here