Picture of Laser Surveillance System for under $20
WARNING: this project involves the use and modification of laser devices. While the lasers I suggest using (store-bought red pointers) are relatively safe to handle, NEVER LOOK DIRECTLY INTO A LASER BEAM, BEWARE OF REFLECTIONS, and be EXTREMELY CAREFUL when MODIFYING a laser product. Also, I am not liable for anything stupid you do.

Using a basic laser pointer and a sensitive amplifier it is possible to listen in on conversations through exterior windows! The price of $20 is simply an estimate, in my case I did not need to buy anything.

The system described in this instructable works on the same principle as commercial projects like this:

NOTE: For a similar projects that may be of interest, check out my blogcheck out my blog. You may find of particular interest the Polarizing Laser Music Mixer!Polarizing Laser Music Mixer!

(Photo of me in the lab, with my own bad-ass glasses, replacing the random military dude who was there before.)
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Step 1: Gather Materials

Picture of Gather Materials
All you need for this project is:

a building with a window to be listened-in on
a laser pointer
a tripod
electrical tape
a magnifying glass
a phototransistor (aka IR detector, can be gotten from remote control recievers)
microphone preamp and amplifier (this can be replaced by a laptop with a MIC port)
an extention chord or batteries for the preamp/amp
someone to listen in on

optional stuff:
a potentiometer (to control the laser brightness)
an infra-red laser (so the light can not be seen)
a digital camera (to see the infra-red laser during calibration)
extra bateries for the laser (upgrade to D cell or something)

(some of the needed equipment is shown below)

Step 2: Attach the Laser to the Tripod

Picture of Attach the Laser to the Tripod
Tightly attach the laser to the tripod with tape. Also tape or rubberband down the power button so that the laser stays on.

In the photo below I also attached wires that run to an external battery pack for extended life.
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skyraper1 year ago
hi , dear ,i am thankful to you for your this work done on this area , i need your help in this project as i am also doing my project in my university but i am doing on IR beam of 980nm and 50mW
i dont know how to detect this IR beam and then after striking on window i.e target how to demodulate this IR beam into audible sound. i seriously need help please
navaburo (author)  skyraper1 year ago
First of all, BE EXTREMELY CAREFUL with IR lasers. 50mW is a LOT of power. That laser can cause serious eye damage, and you won't even know because you can't see it. I strongly recommend that you try this project first with a visible light laser, and only move on to the IR laser if you or someone helping you is experienced with IR radiation and you have taken all the necessary precautions. -- Furthermore, if you are shining this into a building, the people inside will need to know about it to avoid getting eye damage from the laser. It might work well for government spies, but it would really suck to be on the receiving end of a blinding laser. -- I have had some temporary vision loss due to IR in the past, it's no joke.

That said, it is done almost exactly the same way. You just need to adjust the power supply to fit the laser you are using.
Foxtrot702 years ago
I have not tried this but if you are on the same level as the target room both rooms are equipt with crank out casement windows. The entire apt bldg's glass has IR flim on them for heat reflection. The target apt's left window's left halfside is cranked open to 45 degree angle and the right window (observation point next room down) it's right halfside is cranked open to 45 degrees. Now both windows are in alignment facing each other. Sound from one room will reflect into the other via the positioned windows. Hint: the observer must be quiet. If an infrared illuminator coupled with a digital camcorder with Congo Blue filter on the lense is setup. I think you would be able to see into the other apartment's room.
munzer8 years ago
Would one be able to do the same, but in reverse? Could a signal or vibration be sent to the window by the lazer? Could a signal be strong enough to vibrate the window?
_soapy_ munzer7 years ago
No chance. Thermal shock from that much laser would shatter the glass long before any noticeable vibration was set up.
Which is cooler...

stick C4 in any object, light it and it will instantly be cooler.
You can light c4 on fire and heat your coffee or other trail food. It won't explode from just lighting it on fire.
This link isn't direct laser communication but it is a way to transmit data through laser beams (especially sound)

It has only been tested by transmitting sound but other encoded data should work to.
Also this actually is direct communication except it is transmitting data in area of affected particles that cannot be heard (the electromagnetic spectrum)
whilst you cannot rely on the photon momentum to generate vibrations, with a powerful enough laser, one could generate localized heating in certain areas to generate thermal differentials that vary with time. These differentials could generate enough stresses to cause the glass to vibrate. It does however rely on the thermal properties of the medium you want to vibrate and the power of the laser. and you have to have some nicely coordinated movement of the laser to create this thermal wave.
navaburo (author)  munzer8 years ago
in theory, yes. Photons have non-zero momentum. So by relecting light the window does diflect a slight bit. However, you would need a laser so powerful that the window would melt before you were able to move it.
ti can be more stealthy by using infrared laser and ir camera to detect where laser is falling
sorry,grammar error
funny cause you only use 1 laser wire
HevnsDevl3 years ago
I've made basically the same device, only with a crude amplifier (transistor circuit) and headphones instead of the pre-amp; but I keep on hearing feedback although I can clearly hear when the laser shines on the phototransistor. Even while someone is knocking on the glass I still only hear feedback, could it be that I'm saturating the transistor (I've only done this at a range of about 10m) ?
These laser bugs are fun! Here is another nice one...

Now the neighbors are no longer safe!
frogjake94 years ago
Where can I get a microphone preamp?
Djdavies835 years ago
sending 2ch stereo over laser using polarized beams is interesting, the cheap plastic "REAL-D" 3d glasses you get from cinemas for about 75p ($1) would be a start.
 what about the receiver? a kinda 2way mirror at 45D to split the beam in two then use two phototransistors?
navaburo (author)  Djdavies835 years ago
You could use the linear polarization filters from traditional polarized 3D glasses. The Real-3D glasses however use a combination of quarter wave-plates and linear polarization filters to enable decoding of circularly polarized light. So, you are better off using the old (and cheeper) glasses, or ordering a larger sheet of filter from a supplier.

If you want to see a working 2ch system in action, check out my blog post where a few guys and I tried it out. Rough schematics and video included:

Happy Hacking,

Sanctus6 years ago
"If you cannot hear anything, try banging on the window! That should produce a VERY loud sound from the amp." I just imagine the sound AFTER banging on the window: Oh, dear what is that? is that a bird on your 154th floor just banged? Oh no, it's the laser spy just testing their gear! ;)
Or light a c4 parcel, throw it at the window with timing and you'll get what you want.
faruksam6 years ago
(removed by author or community request)
It's not in English.
sooo....use a translator dont just remove it....

Tienes toda la razón!

I mean you are darn right about that, Conrad.

where can i find these damn "audio transformers" ??!! F@*$ links part numbers anything??? somebody help me pleaseeeeeeee
Thos ol' 56Kbps modems; i got mine from there
radio shack $3

Search "audio transformer".

(I am not affiliated with this vendor)
(scumbag lawyers made people start saying that) he he he he he
seanpcurto6 years ago
Question: Can invisible IR lasers be used to do this also? I have some 15mw infrared lasers, I think? but defiantly NOT 625 red or LED) as shown in the 2 pictures (I have 9 of these that slightly vary in specs) Can these be used in place of lasers that operate within the spectrum of visible light? If so so I was thinking of mounting a visible laser along side of it along the same X and Y axis to spot a sight to listen in on without leaving a continuous laser dot on someone's window. (Something to consider carefully BEFORE you select an audio source if you're using visible lasers for this purpose. ) How would IR lasers perform in this application and what modifications if any, would be necessary? If IR lasers work, you could then listen in at night without causing them to duck and crawl for home protection mechanisms :) Any help is appreciated and if I build one, I'll post an instructional on it! Thanks for this awesome instructional navaburo, and I like you pic and lab better the military one. It show that we can pursue our own dreams in our own way without having to kill people.
infrared lasers are quite easy to get hold of - they are the lasers used to read standard cd's. in fact - the blu-ray diode of the ps3 is a triple-stacked diode: 405nm(blue, blu-ray), 660nm(red, dvd), 780nm(red, cd)
Derin bgugi5 years ago
That's only true for backwards-compatible ones.
use a good camera (the kind you take pictures with) to find the IR dot on the window.....
i got a question for you. where can you find an ir laser? any links?
also i have a suggestion. there are some goggles you can make with theatrical gel that lets you see along the ir spectrum here is the link!-For-Under-$10/

let me know what it does if you try it!
navaburo (author)  insmnc!6 years ago
I have infact built those ir goggles. They are pretty cool on a sunny day outside. They will NOT however allow you to see beyond 800nm into the IR. Here is how they work: I. Your eyes can naturally see between 700nm (red) and 400nm (violet) quite well, but are still somewhat sensitive to light in the range of 700nm to 750nm. II. The region of the EM-spectrum between 700nm and a few microns is traditionally called "infrared". III. The goggles block out everything but 700+nm. RESULT: Naturally, you do not notice the ~720nm light because your eye's sensitivity to it is so low, it is drowned out by the other, more visible wavelengths. However, when you are wearing the goggles, all that reaches your eyes is 700+nm light. So, your pupils dilate and you go into your "night vision mode". Dimly through the goggles you will then see everything in a shade of red (that appears grey after using the goggles for some time). This light is all 700+nm so it is officially IR. NOTE!: you will NOT be able to see (most) IR lasers, because (mostly) they work somewhere between 800nm and 1500nm. To see those you will need an IR camera (for near-ish IR, i.e. 800nm, you can just use a consumer-grade point-and-shoot CCD camera).
would be able to see the laser on a bright day if i used my camera? also would 850nm be the best diode to get? and would a cadmium sulfide photocell be responsive to infrared?
navaburo (author)  insmnc!6 years ago
Putting ~10 pieces of Congo Blue theatrical gel in front of the camera lens should make it easy to see the IR light with the camera, even in sunlight. You will have to check the datasheet on the CdS cell to see what its wavelength responce is/
navaburo (author)  seanpcurto6 years ago
Go for it! I see you have some ~850nm diodes, perfect! There should be no modifications necessary, assuming you have a typical photodiode/phototransistor (which has a peak responsiveness of ~900nm). Just keep in mind that IR lasers are VERY dangerous, since you can blind yourself without knowing it is happening! Definitely don't actually shine this into someones window without them knowing. And, for testing/alignment purposes, you can use a standard digital camera to see the IR. (Putting ~10 pieces of Congo Blue theatrical gel in front of the camera lens will make it SUPER easy to see the IR light with the camera.) Tell me how you fare!
It will work but targeting will be much more tricky. Also check the response curve of your phototransistor to make sure it is sensitive for the wavelength of your laser (most phototransistors are sensitive to IR) Also, do not attempt to point this at people, invisible lasers are really dangerous because they do not cause the reflex to look away, and 15mW is quite enough to blind someone.
where do you find ir lazers can you give me a link if you know where
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