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.

Comments

  1. nyeark says:

    sounds like splinter cell to me…

  2. morcheeba says:

    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:

    http://www.questel.orbit.com/EN/contactus/

  3. Paragraph says:

    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.

  4. kris says:

    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.

  5. strider_mt2k says:

    One could use an IR laser if one wanted it to be less “viasable”

  6. So is the Oval Office ;-)

  7. pabloec says:

    Maybe using a nonvisible laser beam in a low EM noise freq?

  8. ryan says:

    could make it a lot less noticeable using an IR laser

  9. TX297 says:

    @#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

  10. rc:line says:

    The RF version gives much better performance:

    http://gbppr.trighost.org/mil/cavity

  11. boooo says:

    In the uk, we cant read http://gbppr.trighost.org/mil/cavity + a few other urls with that site! Bablefish can translate them :-( though, yay thank you bt clean feed.

  12. anti says:

    Hey Boooo (10) – what’s with the “In the uk, we cant read http://gbppr.trighost.org/mil/cavity + a few other urls with that site” I’m in the UK and can read it – or am i missing something really obvious?

  13. Cristal says:

    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.
    Regards
    cristal_4_u

  14. David says:

    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?

  15. IR lasers could be obtained from laser printer carcasses.

  16. Everett says:

    you can still buy the lm387 from a few places even though they aren’t being manufactured anymore. in fact, i bought one from the first google hit for “lm387n”

  17. Retroactive says:

    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,
    retro

  18. andy says:

    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?

  19. hendikfox says:

    maybe andy’s question represents my question too, so it would be nice if you can reply our questions to us…thx

  20. Mikal says:

    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.?

  21. Mikal says:

    i need sincere help from you people …

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