The announcement was made by Ben Nassi, Yaron Pirutin and Boris Zadov, who work at the Ben-Gurion University of the Negev and the Weizmann Institute of Science, near Tel Aviv. The three researchers said they used a low-cost telescope, which they placed nearly 100 feet from a target room containing a commercially available standard light bulb. They then placed each telescope behind a $400 electro-optical sensor. The goal of the contraption was to measure the minuscule changes in light output from the bulb, which are caused by sound vibrations off the bulb’s surface.

The electrical signals captured by the telescopes were digitized using commercially available analog-to-digital converters, before being transferred onto a laptop. The researchers then used commercially available software to filter out noise, and were gradually able to reconstruct clearly audible recordings of the sounds inside the target room. They claim that the resulting recording is clearly audible and can even be transcribed using Google speech-to-text software.

The three Israeli researchers say they now plan to present their findings at the Black Hat security conference in August, which will be held virtually due to health concerns caused by the coronavirus pandemic. Speaking to Wired magazine last weekend, they said that their goal is “not to enable spies or law enforcement, but to make clear to those on both sides of surveillance what’s possible”. “We’re not in the game of providing tools”, they said.