Laser listening device

laser listener

Laser based listening devices work by bouncing the beam off of a window. Sounds in the room cause minute vibrations in the window. These vibrations modulate the laser beam. The laser beam is then converted back into sound at the receiver. Hack-A-Day reader [Aaron v] decided to build one of these devices. It worked, but needs some improvement. He followed plans found here (Coral CDN cache). I’ve also got a local copy of the receiver schematic since there doesn’t seem to be too many of these projects with decent hosting. Williamson Labs has a good discussion of the problems these systems can run into and more advanced setups like interferometry.

22 thoughts on “Laser listening device

  1. I used to work in an office park near Langley, Virginia. On one of the buildings, the windows leaned out at a 30-45 degrees. The top stuck out more than the lower portion of the window, so any laser shined in would be deflected downward. That means anyone spying would have to be in the parking lot to catch the reflected beam AnD MaKe ThAt PeRsOn A lOt MoRe DeTEctABlE.

    The building has lots of tenants. Here’s the best picture I could find — you can barely make out the angled windows:

  2. Well, thats pretty nifty, but there seems to be little to no practicality here. Sure, it’s nifty, but the audio is grainy, the laser is viasable (so it wouldn’t be hard to track the source, especially since your primary target is a window).

    It’s still nifty, and fun to fool around with though.

  3. the cia hq in langley has two sets of glass a certain feet apart from each other specifically to block equipment like this. The laser reflects of the first glass but the vibration is on the second.

  4. @#4 – You’ll find that the CIA HQ also showers their windows in pink noise to scramble anything looking for vibrations.

    Infra-red lasers aren’t terribly expensive either, but it’s still a pretty good concept nonetheless… just needs fine-tuning

  5. Hey guys. I really like this project. I never know you can transform a laser beam to audio. wow. But does anyone know any other site with clear diagram for begenier like me. If you do. please post it.

  6. It looks like the circuit board was prefabricated, was this from a kit?

    Also I looked for some of the parts, namely the preamplifier(LM387) and it seems to be discontinued. Any suggestions for alternatives?

  7. The preamplifier chip is still available at radioshack, I used one for a completely different project though but they had a crap load of them still. That or electronic supply stores might carry them until they arent available anymore period. A long time ago I was thinking about alternative carriers of sound, and thought of this on my own (using laser/light as a carrier of sound) Once I thought of it, I thought this is so f*cking slick someone else must of already thought of it, so I did a few searches and found not only was it thought of but just carrying one around can be considered illegal, heh.
    Anyway Im glad to see that there are still awesome hobbyists out there F*cking around with electronics like I am. Its a lonely life. Later,

  8. hey some friends and i were thinking of building something like this, but we’re confused on what kind of circuitboard it uses…plus we read the schematic and it only lists one serial number for the integrated circuits when there are two…can you help us out with any information concerning the parts and where you found them?

  9. hi, frndz
    i am being working on this project phase 2 i.e instead of red laser i am using IR invisible laser , so kindly can anybody help me in what kind of photodectoctor should i use for IR of 980nm and 50mW laser .
    And what circuitry should i use for demodulation of the reflected IR beam.?

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