Introduction: Laser Surveillance System for Under $20

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.)

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.

Step 3: Rig the Reciever

Picture of Rig the Reciever

Phototransistors work very similarly to microphones in that they vary the current they allow to pass through them when exposed to chaning light levels. So, treat the phototransistor like a mic, and attach it to the MIC port on a laptop, or to the MIC terminals of a preamp, then hook the output of the preamp to the input of an amplifier.

If you are using a preamp, you should be able to screw the leads of the phototransistor right onto the back of the device, but if you are using a laptop, you will need to tape or solder togeather the pins of the phototransistor to the wires of a stripped headphones chord. Remember the ground (-) lead of the phototransistor is the one that has a little flat spot on the plasitc. Look to the photos for help.

Step 4: Position Your Spy Gear

Picture of Position Your Spy Gear

Find a target building and window.

Look at the drawings below to help with the positioning of your gear.
(this only works if you are at the same elevation!)

Step 5: Aim the System

Picture of Aim the System

Stand by the laser tripod. Aim the laser at the window. You should be able to see the reflection of the recieving equipment in the window. If not, reposition the laser or the reciever until you can. If it is dark out, turn a flashlight on near the reciever pointed at the window, that way you can see the reflection in the window and locate the laser appropriately.

Once the laser is aimed, look for the reflected beam/dot near the recieving station. White paper or cardboard (pizza boxes) can come in handy. Position the phototransistor in the beam.

Step 6: Magnify

Picture of Magnify

Position a magnifying glass in front of the phototransistor, in an attempt to focus the beam. You should hear the most noise from the amp when it is positioned correctly.

At this point you may need to adjust the volume on the amp and preamp. Turn it up until you hear feedback, then turn it down until it goes away.

Step 7: Give It a Try - Taking It Further

Listen for voices. You should be able to hear the low frequencies of any conversation inside the room of the targeted window. If you cannot hear anything, try banging on the window! That should produce a VERY loud sound from the amp.

If you get this project to work, the worst thing you could do is stop there! Try to build on the project. Try more than one laser, or getting more distance, or whatever comes to mind. One thing I have done to extend the project is to send music over the laser beam, and even sending two channels of music using two lasers polarized at right-angles to one another.

Feel free to leave some comments.
Happy experimenting!


PopsicleGhoul (author)2015-08-16

Wow, super cool build! Will this work on double-paned windows (like ones for cold climates)? Also, will the subjects of your surveillance be able to see a laser dot? Thank you.

skyraper (author)2013-04-14

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)skyraper2013-04-14

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.

Foxtrot70 (author)2012-06-07

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.

munzer (author)2006-09-22

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_ (author)munzer2007-08-29

No chance. Thermal shock from that much laser would shatter the glass long before any noticeable vibration was set up.

beehard44 (author)_soapy_2010-02-11

Which is cooler...

stick C4 in any object, light it and it will instantly be cooler.

stormy0314 (author)beehard442012-06-07

You can light c4 on fire and heat your coffee or other trail food. It won't explode from just lighting it on fire.

curecreator (author)munzer2009-01-25

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)

Capricorn.san (author)munzer2007-08-09

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)munzer2006-09-29

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.

Suraj Grewal (author)2012-06-07

ti can be more stealthy by using infrared laser and ir camera to detect where laser is falling

sorry,grammar error

Dusk Shadows (author)2012-06-07

funny cause you only use 1 laser wire

HevnsDevl (author)2012-01-05

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) ?

AbaddonSpirit (author)2010-09-24

These laser bugs are fun! Here is another nice one...

Now the neighbors are no longer safe!

frogjake9 (author)2010-05-20

Where can I get a microphone preamp?

Djdavies83 (author)2010-03-25

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)Djdavies832010-03-25

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,

Sanctus (author)2008-06-24

"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! ;)

beehard44 (author)Sanctus2010-02-11

Or light a c4 parcel, throw it at the window with timing and you'll get what you want.

bowmaster (author)2008-11-16

It's not in English.

conrad2468 (author)bowmaster2009-03-17

sooo....use a translator dont just remove it....

stormende (author)conrad24682010-01-17


Tienes toda la razón!

I mean you are darn right about that, Conrad.


mikemmcmeans (author)2008-01-12

where can i find these damn "audio transformers" ??!! F@*$ links part numbers anything??? somebody help me pleaseeeeeeee

Colonel88 (author)mikemmcmeans2009-08-16

Thos ol' 56Kbps modems; i got mine from there

radio shack $3

legionlabs (author)mikemmcmeans2008-06-24

Search "audio transformer".

(I am not affiliated with this vendor)

conrad2468 (author)legionlabs2009-03-17

(scumbag lawyers made people start saying that) he he he he he

seanpcurto (author)2008-04-18

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.

bgugi (author)seanpcurto2008-06-26

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 (author)bgugi2009-05-29

That's only true for backwards-compatible ones.

conrad2468 (author)seanpcurto2009-03-17

use a good camera (the kind you take pictures with) to find the IR dot on the window.....

insmnc! (author)seanpcurto2008-07-30

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!2008-07-30

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).

insmnc! (author)navaburo2008-07-30

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!2008-07-31

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)seanpcurto2008-07-30

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!

MrPhelps (author)seanpcurto2008-06-24

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.

honsoworld-bro (author)2009-05-21

where do you find ir lazers can you give me a link if you know where

junits15 (author)2009-04-05


JohnJY (author)2008-08-14

Ok you guys will think this is funny. If you know your being spyed on just constently move the window. These things work by feeling vibrations. So but somthing that buzzes on the window.

Delvie (author)JohnJY2009-02-06

There was an episode of Burn Notice where they knew they were being listened to by laser so they taped a turned on vibrator to the window.

conrad2468 (author)Delvie2009-03-17

how appropriate........

alexh934 (author)2009-02-25

Do you need the radioshack circuit board kit to make this? and is that a 50k ohm linear taper potentiometer? And i cannot find an infared laser, will red work?

navaburo (author)alexh9342009-02-25

No, you don't need the radioshack board. It was just a convinient platform to build upon. And I would recommend using a RED laser first, because infrared lasers can be dangerous (You can't tell when your eyes are being damaged!). - Good luck!

sam noyoun (author)2007-03-31

A few questions (they might be silly ones, I don't know, I'm not very scientifically minded...): - What if you shone your laser through an infrared filter? I guess what I mean is: do green/red lasers emit any infrared light that could be filtered? - If I were to use processed negative film as an infrared filter, would the laser burn a hole through it? - What strength lased did you use? - Would plugging the mic. jack into a MP3 player, rather than a laptop still work?

navaburo (author)sam noyoun2007-04-07

- lasers only emit a single wavelength of light, so a green laser emmits only a negligable amount of infrared.
- depends on the strength of the laser (a laser pointer shown here, definately not)
- I went into staples, office depo, and wallmart and looked at their laser pointers. Then i bought the cheepest one i could find that was actually a laser (some of the "laser pointers" just have a red led and their beam diverges very fast, so it is useless). Long story short, a rather weak laser.
-the MIC output from the laser reciever needs to goto an amplifier or pick-up of some sort. Plugging it into an MP3 player will do nothing.
However, you _can_ use the MP3 player's signal to modulate the laser beam at the transmitter, and you will hear the music at the reciever. For that, look at this project:

> they might be silly ones, I don't know, I'm not very scientifically minded...
they are good questions nonetheless. what good is a scientist if he keeps his mouth shut.

BlueFusion (author)navaburo2007-05-23

"- lasers only emit a single wavelength of light, so a green laser emmits only a negligable amount of infrared." This is quite plainly rubbish. Sorry to be so frank. Green laser diodes do not exist; instead an infrared laser diode is used. This is called DPSSFD technology. (Diode Pumped Solid State Frequency Doubled) An infrared laser at 802nm pumps a tiny block of Nd:YAG to double the frequency to 532nm. Therefore unless it is a quality green laser it will not have an infrared filter inside it to remove the infrared that can be emitted. A supposedly green laser can generate 80% IR and only 20% visible green light. Also a laser needs to be at least 50mW before it will burn stuff. A cheapie laser (<$30) won't burn anything. Also a red laser will only emit a negligible amount of IR as a laser diode can easily produce light at 652nm. (red laser light) Also if you are wondering how doubling the frequency halves the number: Imagine a sine wave. If you make the peaks twice as close together the distance between them is half as much. Or, imagine a line of bricks (or anything). Say they're 30cm apart. If you make them only 15cm apart (doubling the 'frequency' or how often they are there if you walked past them) the distance is halved. Sorry for the long comment.

Tinderbox (author)BlueFusion2009-01-22

it may just be a typo pal, but you don't measure frequency in metres, you measure it in Hertz (Hz), wavelength is measured in metres (and naturally, nanometres as you get down to these levels). Again, apologies if you mistyped that, but it's fairly important.

About This Instructable




Bio: I am a student and hobbiest. I'm into physics, linguistics, sailing, electronics, hacking (not cracking), music, and the like. I post most of my ... More »
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