“I think I’ve created the first modulated laser microphone in the radio frequency domain,” Kamkar says. “Once I have a radio signal, I can treat it like a radio and I can take advantage of all the tools that exist for radio communication.” In other words, Kamkar turned sound into light and then into radio, and then back into sound.
Samy Kamkar at his home office.Photography: Roger Kisby
For his keystroke detection technique, Kamkar fed the output of his laser microphone into an audio program called iZotopeRX to further remove noise and then into an open-source software called Key 3 that can convert the sound of keystrokes into readable text. In fact, security researchers have shown for years that keystroke audio, recorded from a nearby microphone, can be analyzed and deciphered to yield the text a surveillance target is typing by distinguishing small acoustic differences in various keys. One group of researchers has shown that even relatively accurate text can be derived from keystroke sounds. recorded during a Zoom call.
However, Kamkar was more interested in the 2009 Defcon demo in which security researchers Andrea Barisani and Daniele Bianco showed they could use a simple laser microphone to roughly detect words typed on a keyboard — a trick that would enable long-distance spying. In that demo, the two Italian hackers went so far as to test their laser spying technique across the room from a laptop and generate a list of possible word pairs that matched the vibration signature they had recorded.
Speaking to WIRED, Barisani says his experiment was just a “quick and easy” proof of concept compared to Kamkar’s more polished prototype. “Samy is brilliant and there was a lot of room for improvement,” Barisani says. “I’m 100 percent confident that he could improve our attack both in hardware setup and signal processing.”
Kamkar Laser Spy Kit: An Infrared Laser…Photography: Roger Kisby
…connected to an oscilloscope signal generator, current controller, temperature controller and amplifier power supply.Photography: Roger Kisby
Kamkar’s results appear to be much better: Some samples of text he recovered by typing with his laser microphone and shared with WIRED were almost completely legible, with only a letter missing every word or two; others showed somewhat more spotty results. Kamkar’s laser microphone worked well enough to detect keystrokes—in fact, he also tested using it to record audio in a room more generally, bouncing its infrared laser off a window. It produced remarkably clear sound, noticeably better than other samples of the laser microphone audio posted online, at least among those stealthily recorded from window vibrations.
Of course, since laser microphones have been around for decades, Kamkar admits he doesn’t know what advances the technology may have made in commercial implementations available to governments or law enforcement, let alone even more secretive and custom technologies potentially created or used by intelligence agencies. “I assume they’re doing this or something like it,” Kamkar says.
Unlike the creators of such professional spy tools, however, Kamkar publishes the complete schematics of his homemade laser microphone spy kit. “Ideally, the public should know everything that intelligence agencies are doing and also what is coming next,” Kamkar says. “If you don’t know that something is possible, you probably won’t protect yourself against it.”