Fluorescent lamps (don't) have ears: a TSCM myth is busted
A former technical surveillance countermeasures (TSCM) sweeper revisits a claim from his training: that fluorescent lamps can passively eavesdrop on conversations. After explaining the physics and his testing setup—a 200 W audio system, high-speed photography, and a 9-inch tube—he finds no visible artifacts. The myth, he concludes, is busted for practical purposes.
In terms of a practical attack, I think the myth is busted. Sorry, Mr. Bond?
- butvacuum
Everybody is focused on the tubes... What about the diffuser with pyramid shaped lenses? the highly directional light projects a beam (flourescent lights are known for awfully harsh shadows) through the thin, lightweight 24x24" or 24x48" lens(diffuser). as the light is projected down a minimum of 8 feet the tiny deflection from sound hitting the diffuser is amplified. Then, at an interface of light and shadow on the floor, the moving projection becomes a brightness signal that has audio encoded in it. they could use a lens and a photodiode. Didn't exactly have 5000fps cameras falling off trees 40 years ago.
- _kb
If you get a high frame rate video of a space, there's plenty of other objects that can act as visual transducers: https://people.csail.mit.edu/mrub/VisualMic/.
- floxy
I as skeptical as the next guy when it comes to the claim that ambient audio modulates the fluorescent light. But I could sure use more details on what analysis was done to the photos. Sounds like there were several photos taken, say 100ms(?) apart. Then the photos were subtracted pixel-by-pixel to look at the variations in time (between photos) or spatially (neighboring pixels)? I still think a photo-diode AC-coupled to a high gain amplifier fed into an oscilloscope would be the more conclusive test. Do a audio frequency sweep from 100-10kHz. Both with the fluorescent light on, and then again with the light off (as a control, in case something else in the setup is sensitive to the audio).