HOW TO: Make a Laser Espionage Microphone


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Here’s a short video that will show you how to make a simple laser listening device that will allow you to listen inside of buildings hundreds of feet away from you. Enjoy!





137 Responses to HOW TO: Make a Laser Espionage Microphone

  1. What I didn't get was at about the 78 second mark of the video – how to you get the laser beam to bounce back from the window to the photocell? I understood that correctly, didn't I?

  2. What I didn’t get was at about the 78 second mark of the video – how to you get the laser beam to bounce back from the window to the photocell? I understood that correctly, didn’t I?

  3. I am guessing that you can use a big sheet of white paper to try and see where the laser dot reflects to (easier than hunting around with the photocell). When you see the reflected dot, position the second tripod there/

  4. I am guessing that you can use a big sheet of white paper to try and see where the laser dot reflects to (easier than hunting around with the photocell). When you see the reflected dot, position the second tripod there/

      • I’d heard about this project, and I’d read about transmitting sound with laser, but I didn’t know it was this simple to get it bounce off of glass. I’ll try this for sure…

        I think the music is rather Layenda by Albeniz Asturias :) I may be wrong…

  5. That is interesting, you could make a small white parabolic dish with the cell in the middle to help focus the beam onto the cell. Not sure if that would improve the device but makes it look more 007 like.

  6. That is interesting, you could make a small white parabolic dish with the cell in the middle to help focus the beam onto the cell. Not sure if that would improve the device but makes it look more 007 like.

  7. Yeah, Hole Wheet, Albeniz shamelessly ripped off The Doors and probably didn't even give them credit. Shame on him …. someone should sue.

  8. Yeah, Hole Wheet, Albeniz shamelessly ripped off The Doors and probably didn’t even give them credit. Shame on him …. someone should sue.

  9. Cool device but not very practical. Would be easier to use a wireless transmitter instead of the laser.

    I also imagine it would get a lot of interference from the ambient noise.

    • 1) With a wireless, you have to go and plant the bug…not always easy, if even doable.

      2) If you understand the concept, you will come to the conclusion that there cannot be any ambient noise…the receiving aparatus deals with light, not compression and rarefraction of air such as a microphone requires.

      Danny

      • @Daniel Doucet

        Actually, there can, and usually is ambient noise. Depending on how large, far away from the subject, thick, steady the glass object is, there can be quite a bit of undesired noise. I've done this a few times and it's rare to get it perfect.

        Also, it's not rarefraction, it's rarefaction… and yes, it does deal with compression and rarefaction, it just uses glass as the sounding board. Light is merely the transmitter of analog information from vibrating medium: glass.

    • Not so, the FBI has been using this technology for years, it's a lot easier to record someone from a high rise, or similar, apartment. Instead of having to have actual physical access to the site, they can bounce a laser off of the window, from another building, I'm sure it gets lost somewhere in the laws of wiretapping too, but don't take my word on that, I just think the feds are spooky.

  10. Cool device but not very practical. Would be easier to use a wireless transmitter instead of the laser.

    I also imagine it would get a lot of interference from the ambient noise.

    • 1) With a wireless, you have to go and plant the bug…not always easy, if even doable.

      2) If you understand the concept, you will come to the conclusion that there cannot be any ambient noise…the receiving aparatus deals with light, not compression and rarefraction of air such as a microphone requires.

      Danny

      • @Daniel Doucet

        Actually, there can, and usually is ambient noise. Depending on how large, far away from the subject, thick, steady the glass object is, there can be quite a bit of undesired noise. I’ve done this a few times and it’s rare to get it perfect.

        Also, it’s not rarefraction, it’s rarefaction… and yes, it does deal with compression and rarefaction, it just uses glass as the sounding board. Light is merely the transmitter of analog information from vibrating medium: glass.

    • Not so, the FBI has been using this technology for years, it’s a lot easier to record someone from a high rise, or similar, apartment. Instead of having to have actual physical access to the site, they can bounce a laser off of the window, from another building, I’m sure it gets lost somewhere in the laws of wiretapping too, but don’t take my word on that, I just think the feds are spooky.

  11. I have to wonder how much of a reflection you'd get from window glass – the most noticeable property of which is that it lets light pass through it. Some direct reflection sure, but as much as was portrayed in the video?

    • Glass reflects pretty well when light hits it at an angle (Snell's law and all), which is maybe why the sensor and laser weren't closer together in the set-up they showed.

  12. I have to wonder how much of a reflection you’d get from window glass – the most noticeable property of which is that it lets light pass through it. Some direct reflection sure, but as much as was portrayed in the video?

    • Glass reflects pretty well when light hits it at an angle (Snell’s law and all), which is maybe why the sensor and laser weren’t closer together in the set-up they showed.

  13. This does work, and was a Popular Electronics project in 1988 or so. The laser I built then was Heathkit's, and I scratch built the listener.

    Yeah, for a bail bondsman to snoop on bail jumpers to try to hear how many folks were home.

    The glass reflects a good part of the laser, and it also works for shorter distances bouncing back off of doors, aluminum siding, or the metal of house trailers and metal buildings. All vibrate to voices. And, music, water running, the sounds of home making… A major problem is stability of both devices, and keeping them aligned. Vehicle mounting is subject to harmonic vibrations introducing losses in sound if engine is idling.

    If desperate enough, this is a non-intrusive surveillance device, that can help determine if someone is home, and actually record their voices.

    For the folks enforcing bail, etc. no more problem than photographing in public, or from the public streets. When used against bail jumpers or escaped convicts, this is one thing that helps protect everyone.

    Yes, I run GNU/Linux, and advocate Open Source and Creative Commons, so these kinds of circuits are available to all.

  14. This does work, and was a Popular Electronics project in 1988 or so. The laser I built then was Heathkit’s, and I scratch built the listener.

    Yeah, for a bail bondsman to snoop on bail jumpers to try to hear how many folks were home.

    The glass reflects a good part of the laser, and it also works for shorter distances bouncing back off of doors, aluminum siding, or the metal of house trailers and metal buildings. All vibrate to voices. And, music, water running, the sounds of home making… A major problem is stability of both devices, and keeping them aligned. Vehicle mounting is subject to harmonic vibrations introducing losses in sound if engine is idling.

    If desperate enough, this is a non-intrusive surveillance device, that can help determine if someone is home, and actually record their voices.

    For the folks enforcing bail, etc. no more problem than photographing in public, or from the public streets. When used against bail jumpers or escaped convicts, this is one thing that helps protect everyone.

    Yes, I run GNU/Linux, and advocate Open Source and Creative Commons, so these kinds of circuits are available to all.

  15. Two years ago, a couple guys in the physics club at my college built something like this, only they used a split photo detector and they had a lot more circuitry. I'm not sure if it was all just audio amplification stuff or what, but it was pretty sweet.

  16. Two years ago, a couple guys in the physics club at my college built something like this, only they used a split photo detector and they had a lot more circuitry. I’m not sure if it was all just audio amplification stuff or what, but it was pretty sweet.

  17. I wonder if you could also use a small telescope mounted on a tripod to zoom in on the spot where the laser hits the window. After finding the dot, just tape the sensor on the eyepiece? Maybe then you could still listen without having to be right near where the laser reflects? Mmmmaybe? Perhaps? Eh?

    • I was thinking, that might work better if you pointed the red dot on something more opaque, but something that may still be kind-of "resonant". I imagine the brighter the dot, the better, and the less amount of other ambient light, the better. It might also be good if it was pointed somewhere where somebody doesn't notice a little red dot coming from nowhere. That's probably the most important thing.

    • If you look at the laser dot reflection through a telescope it could burn your retina. Don't do that w/o protective goggles.

  18. I wonder if you could also use a small telescope mounted on a tripod to zoom in on the spot where the laser hits the window. After finding the dot, just tape the sensor on the eyepiece? Maybe then you could still listen without having to be right near where the laser reflects? Mmmmaybe? Perhaps? Eh?

    • I was thinking, that might work better if you pointed the red dot on something more opaque, but something that may still be kind-of “resonant”. I imagine the brighter the dot, the better, and the less amount of other ambient light, the better. It might also be good if it was pointed somewhere where somebody doesn’t notice a little red dot coming from nowhere. That’s probably the most important thing.

    • If you look at the laser dot reflection through a telescope it could burn your retina. Don’t do that w/o protective goggles.

  19. Infrared laser eliminates the noticeable red dot in the target's room, but makes it a royal pain in the ass to get the reflection.

    And no, kirby, pointing a telescope at the red dot on the opaque surface probably won't do it. Shine a laser at a mirror 100 yards away. Now, turn the mirror just a degree, and the reflected point moves by several feet. replace the mirror with an opaque surface and point the telescope at it. Even if you turn the opaque surface 90 degrees, the telescope will still be focused on the red dot.

    The mirror/window is necessary to modulate the steady laser signal, and the photodiode picks up that modulation.

  20. Infrared laser eliminates the noticeable red dot in the target’s room, but makes it a royal pain in the ass to get the reflection.

    And no, kirby, pointing a telescope at the red dot on the opaque surface probably won’t do it. Shine a laser at a mirror 100 yards away. Now, turn the mirror just a degree, and the reflected point moves by several feet. replace the mirror with an opaque surface and point the telescope at it. Even if you turn the opaque surface 90 degrees, the telescope will still be focused on the red dot.

    The mirror/window is necessary to modulate the steady laser signal, and the photodiode picks up that modulation.

  21. Using an infrared laser wouldn't be so hard if you have a Sony camcorder with NightShot. In NightShot mode, the IR filter is removed so infrared light shows up very well in the camera's viewfinder (and film, of course). So while you couldn't see it with your eyes, the camcorder would at least make it possible to align them.

    Now, where can we get low cost infrared lasers? I thought I read somewhere that many lasers start out as IR lasers, but they put a crystal in the laser's path to change the frequency to the visible spectrum or something like that. Maybe it would be as simple as removing a crystal?

  22. Using an infrared laser wouldn’t be so hard if you have a Sony camcorder with NightShot. In NightShot mode, the IR filter is removed so infrared light shows up very well in the camera’s viewfinder (and film, of course). So while you couldn’t see it with your eyes, the camcorder would at least make it possible to align them.

    Now, where can we get low cost infrared lasers? I thought I read somewhere that many lasers start out as IR lasers, but they put a crystal in the laser’s path to change the frequency to the visible spectrum or something like that. Maybe it would be as simple as removing a crystal?

  23. Reposting my comment from elsewhere:

    Hmm, it looks like if your target is 200 ft away and your beam is even one degree off perpendicular to the surface of the glass, your laser and your detector will have to be roughly 7 feet apart. So if you want to use this from "hundreds of feet away", it'll be really inconvenient unless you're damn close to perpendicular.

    And now it occurs to me that there's kind of a rock and a hard place thing going on here: for this to be convenient, you want to be very close to perpendicular but the reflection will be stronger the farther from perpendicular you are. Hmm…

  24. Reposting my comment from elsewhere:

    Hmm, it looks like if your target is 200 ft away and your beam is even one degree off perpendicular to the surface of the glass, your laser and your detector will have to be roughly 7 feet apart. So if you want to use this from “hundreds of feet away”, it’ll be really inconvenient unless you’re damn close to perpendicular.

    And now it occurs to me that there’s kind of a rock and a hard place thing going on here: for this to be convenient, you want to be very close to perpendicular but the reflection will be stronger the farther from perpendicular you are. Hmm…

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  26. Thats pretty cool, I didnt realize you could do that. Really though, its hardly suited for espionage… wouldnt you have to do a lot of positioning of things beforehand? How could this be used practically?

  27. Thats pretty cool, I didnt realize you could do that. Really though, its hardly suited for espionage… wouldnt you have to do a lot of positioning of things beforehand? How could this be used practically?

  28. My microphone cable doesn't have a black, red, white combination, what should I do?

    (One have one white besides one live and one red besides one live)

    (Another have a green, a copper reddish, a copper yellowish and a green-copper stripped)

  29. My microphone cable doesn’t have a black, red, white combination, what should I do?
    (One have one white besides one live and one red besides one live)
    (Another have a green, a copper reddish, a copper yellowish and a green-copper stripped)

  30. During the Cold war, the Soviets used this type of technology against the USA. Eventually, Langley was built with this in mind. they have an outer barrier of windows and concrete so that someone can't listen in with this type of device.

  31. During the Cold war, the Soviets used this type of technology against the USA. Eventually, Langley was built with this in mind. they have an outer barrier of windows and concrete so that someone can’t listen in with this type of device.

  32. I call BS too. I am an electronics technician and I can tell you that your computer's sound card will not get anything intelligent out of a photocell by itself. Maybe if there was a lot more circuitry involved…but not a photocell and some wire. This would be what you call…an internet hoax. Also, note the VERY POOR soldering job these kids did on their "project" (although I feel the real project is to see how many idiots they can get to try this).

    • ME:

      Have you personally tried this? I just did it last night and it worked. Lots of hissing sound but can make out the conversation behind the glass. It does work.

      The author of the video clip probably used some software the filter the sound clip.

  33. I call BS too. I am an electronics technician and I can tell you that your computer’s sound card will not get anything intelligent out of a photocell by itself. Maybe if there was a lot more circuitry involved…but not a photocell and some wire. This would be what you call…an internet hoax. Also, note the VERY POOR soldering job these kids did on their “project” (although I feel the real project is to see how many idiots they can get to try this).

    • ME:

      Have you personally tried this? I just did it last night and it worked. Lots of hissing sound but can make out the conversation behind the glass. It does work.

      The author of the video clip probably used some software the filter the sound clip.

  34. Jesus Christ – not only does the author of this video sound horrifically gay, he also speaks as though mentally deficient. Upsetting.

  35. Jesus Christ – not only does the author of this video sound horrifically gay, he also speaks as though mentally deficient. Upsetting.

  36. I'm glad that most posters on here are mentally deficient.

    Way to go guys! Here's a cookie for attempting to type something worth reading!

  37. I’m glad that most posters on here are mentally deficient.

    Way to go guys! Here’s a cookie for attempting to type something worth reading!

  38. Earlier…

    Comment by SuperBadDolomite

    2007-08-17 22:02:57

    Yeah, Hole Wheet, Albeniz shamelessly ripped off The Doors and probably didn’t even give them credit. Shame on him …. someone should sue.

    I'm thinking that SuperBadDolomite meant this comment tongue-in-cheek, but if he/she didn't, then here's the real info on that guitar piece.

    It was originally written by Isaac Albeniz (1860-1909) for the piano. The original name was "Preludio", and was published as "Asturias" (the northern mining region in Spain) and subtitled "Leyenda" (Legend) after Albeniz's death. More information at http://www.stanleyyates.com/articles/albeniz/leye….

    The intro riff for Spanish Caravan by the Doors sounds supsiciously like Asturias-Leyenda, though apparently Robbie Krieger disputed this allegation when asked it directly by a caller on a radio program (http://www.songfacts.com/detail.php?id=241 first comment). Not sure how reliable that source is though, and frankly the start of the song looks like it was indeed stolen from this classical piece (in my opinion – and I'd never heard it before today, though I do know the classical piece well).

    So, to assert that the Doors should sue Albeniz, who died close to 37 years before Robbie Krieger was born, is either quite humorous, or shows abject ignorance.

    I'll presume the best, and take it as a joke. :)

  39. Earlier…

    Comment by SuperBadDolomite

    2007-08-17 22:02:57

    Yeah, Hole Wheet, Albeniz shamelessly ripped off The Doors and probably didn’t even give them credit. Shame on him …. someone should sue.

    I'm thinking that SuperBadDolomite meant this comment tongue-in-cheek, but if he/she didn't, then here's the real info on that guitar piece.

    It was originally written by Isaac Albeniz (1860-1909) for the piano. The original name was "Preludio", and was published as "Asturias" (the northern mining region in Spain) and subtitled "Leyenda" (Legend) after Albeniz's death. More information at http://www.stanleyyates.com/articles/albeniz/leye….

    The intro riff for Spanish Caravan by the Doors sounds supsiciously like Asturias-Leyenda, though apparently Robbie Krieger disputed this allegation when asked it directly by a caller on a radio program (http://www.songfacts.com/detail.php?id=241 first comment). Not sure how reliable that source is though, and frankly the start of the song looks like it was indeed stolen from this classical piece (in my opinion – and I'd never heard it before today, though I do know the classical piece well).

    So, to assert that the Doors should sue Albeniz, who died close to 37 years before Robbie Krieger was born, is either quite humorous, or shows abject ignorance.

    I'll presume the best, and take it as a joke. :)

  40. I would think the best way to do this would be with an IR laser mounted on a tripod with a red laser for aiming purposes in line with it. THen you could get the photocell lined up with the red laser, and turn it off, using the IR for picking up the vibrations. I'm not sure how they do it with the professional models, but I know they filter out ambient sound, I.E. A/C running or something like that. The software just cancels out any background noise that is vibrating the window in at a set freq.

    • Professional models don't use lasers because of the necessary beam angularity. That would require you to be in a precise location to receive the bounce and you could be spotted making those obvious setup adjustments. Additionally, lasers don't function well on large windows during wind or close to traffic or on most high rise buildings. The glass actually can have significant movement under these conditions making reception difficult or sketchy. I know because my group attempted laser surveillance and found it too limiting. The federal boys prefer the small focused microphones.

      Regardless, those who suspect they are being watched or listened to will always divert or confuse the interior sound. This is rather easily done but there are still ways to pick up voices from a considerable distance. By the way, running water is not totally effective against the federal equipment.

  41. I would think the best way to do this would be with an IR laser mounted on a tripod with a red laser for aiming purposes in line with it. THen you could get the photocell lined up with the red laser, and turn it off, using the IR for picking up the vibrations. I’m not sure how they do it with the professional models, but I know they filter out ambient sound, I.E. A/C running or something like that. The software just cancels out any background noise that is vibrating the window in at a set freq.

    • Professional models don’t use lasers because of the necessary beam angularity. That would require you to be in a precise location to receive the bounce and you could be spotted making those obvious setup adjustments. Additionally, lasers don’t function well on large windows during wind or close to traffic or on most high rise buildings. The glass actually can have significant movement under these conditions making reception difficult or sketchy. I know because my group attempted laser surveillance and found it too limiting. The federal boys prefer the small focused microphones.

      Regardless, those who suspect they are being watched or listened to will always divert or confuse the interior sound. This is rather easily done but there are still ways to pick up voices from a considerable distance. By the way, running water is not totally effective against the federal equipment.

  42. I would think the best way to do this would be with an IR laser mounted on a tripod with a red laser for aiming purposes in line with it. THen you could get the photocell lined up with the red laser, and turn it off, using the IR for picking up the vibrations. I’m not sure how they do it with the professional models, but I know they filter out ambient sound, I.E. A/C running or something like that. The software just cancels out any background noise that is vibrating the window in at a set freq.

  43. All this reflection discussion would be solved by taping a small mirror to the door and picking up the reflection. This would also eliminate the red dot inside. Am I right? Did anybody try this?

  44. All this reflection discussion would be solved by taping a small mirror to the door and picking up the reflection. This would also eliminate the red dot inside. Am I right? Did anybody try this?

    • Yes, 'range' mikes are often available in specialty stores for under $70. They don't use lasers as the setup is difficult because of the angles and beam reception required. Recommendation: Get a used federal unit off ebay or from specialty stores. They last forever because of the simplicity and good sound editing software will remove the harmonics or the ambient noise patterns.

    • Yes, ‘range’ mikes are often available in specialty stores for under $70. They don’t use lasers as the setup is difficult because of the angles and beam reception required. Recommendation: Get a used federal unit off ebay or from specialty stores. They last forever because of the simplicity and good sound editing software will remove the harmonics or the ambient noise patterns.

  45. I am confused. Was there an earlier video I missed on how to convert a laser pointer to a microphone?

    I see a wire coming out the back of the laser pointer.

  46. I am confused. Was there an earlier video I missed on how to convert a laser pointer to a microphone?

    I see a wire coming out the back of the laser pointer.

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  48. Although this functions reasonably well as a long range amplified mike, it lacks some adjustibility and is fairly easy to spot because of the necessarily perfect angular positioning. In short, if you are in a car, you would need to park precisely to receive the return beam. That could make you noticeable.

    You can make an adjustable distance microphone almost as easily, but somewhat more expensively. It does produce harmonic distortions and pick up ambient sounds that need to be removed via sound editing software, but a true distance (or 'range') microphone is considered best for most covert surveillance situations. They can be hand held, are small and easily concealed, usually operate on 12 volts, and plug into the cigarette lighter socket. We used them very effectively in federal surveillance of racketeering suspects.

  49. Although this functions reasonably well as a long range amplified mike, it lacks some adjustibility and is fairly easy to spot because of the necessarily perfect angular positioning. In short, if you are in a car, you would need to park precisely to receive the return beam. That could make you noticeable.

    You can make an adjustable distance microphone almost as easily, but somewhat more expensively. It does produce harmonic distortions and pick up ambient sounds that need to be removed via sound editing software, but a true distance (or ‘range’) microphone is considered best for most covert surveillance situations. They can be hand held, are small and easily concealed, usually operate on 12 volts, and plug into the cigarette lighter socket. We used them very effectively in federal surveillance of racketeering suspects.

  50. About aiming, why not use a red laser to aim, then use the infrared laser to listen in? With a little work, the two lasers could be aligned to each other. A second or two shot of the red laser, adjust the mic, another second or two then adjust again, cheap alternative to buying a camera. Of course if you are really into spy work…………….

  51. About aiming, why not use a red laser to aim, then use the infrared laser to listen in? With a little work, the two lasers could be aligned to each other. A second or two shot of the red laser, adjust the mic, another second or two then adjust again, cheap alternative to buying a camera. Of course if you are really into spy work…………….

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  53. ive tried to do this and i have everything needed. got a cadmium sulfide ldr (photocell), but its aint working… do u need a specific type of cds, with a specific type of resistance or wateva??? and i cant find headphone wire with 3 inner wires, only ones with 2 or 4 wires??? does the reflected laser dot have to cover the entire surface of the photocell , coz mine only covers a small area?? pls help, need to get this working

  54. ive tried to do this and i have everything needed. got a cadmium sulfide ldr (photocell), but its aint working… do u need a specific type of cds, with a specific type of resistance or wateva??? and i cant find headphone wire with 3 inner wires, only ones with 2 or 4 wires??? does the reflected laser dot have to cover the entire surface of the photocell , coz mine only covers a small area?? pls help, need to get this working

  55. it doesn't work for me!!! please tell me if you have to buy the headphones from america cos both the headphones i've tried have got a copper coloured wire, a blue coloured wire and a green coloured wire!!! please sum1 tell me how to wire it if u know with these colours and if i have to buy dem from AMERICA!!!!!!!!!!!!!!!!!!!!!!!!!!!

  56. it doesn’t work for me!!! please tell me if you have to buy the headphones from america cos both the headphones i’ve tried have got a copper coloured wire, a blue coloured wire and a green coloured wire!!! please sum1 tell me how to wire it if u know with these colours and if i have to buy dem from AMERICA!!!!!!!!!!!!!!!!!!!!!!!!!!!

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  58. when i made i thought it was amazing that it actually works so i brought it in for a science fair at my school.

  59. when i made i thought it was amazing that it actually works so i brought it in for a science fair at my school.

  60. Why do you even need the laser? Why not just focus the photo cell on the window. If this BS truly worked the photocell should be able to use sun light or the houses internal light to pick up vibes off the glass, thus translating the vibes into audio. As much as I want to believe this, I have to call BS.

    • Internal light and sun light is a diffuse reflection you need specular reflection in order for this to work

  61. Why do you even need the laser? Why not just focus the photo cell on the window. If this BS truly worked the photocell should be able to use sun light or the houses internal light to pick up vibes off the glass, thus translating the vibes into audio. As much as I want to believe this, I have to call BS.

    • Internal light and sun light is a diffuse reflection you need specular reflection in order for this to work

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  63. Can we use any kind of photocell? IS there any kind that is or isn’t “powerful” enough?
    A photocell only transforms the light into a resistance, but I don’t understand how the resistance can be transformed into sound!
    Please can somebody help me I’m really desperate!

  64. Can we use any kind of photocell? IS there any kind that is or isn't "powerful" enough?

    A photocell only transforms the light into a resistance, but I don't understand how the resistance can be transformed into sound!

    Please can somebody help me I'm really desperate!