Have you ever needed to hear a conversation in a room you are unable to access or bug easily? If so, and if that room has a window, you can using a laser microphone.

A laser microphone is a device that uses the vibrations of a window or similar pane of glass or plastic to record sounds near said window. A laser is pointed at a window and a photocell is placed where the laser's reflection lands. That photocell is then connected to a recording device. The vibrations of the eindow causes slight movements in the laser's reflection which, in turn, cause small fluxuations in the photocell microphone's current. This may seem complicated but it can be done cheaply and easily.

Step 1: Things Needed

The things you need for this build are very easily obtained and cost me about $10.

Soldering gun( or just electrical tape if you're being really cheap)
Scissors( if you're using headphones)

A laser pointer $1.50
A photocell $.30
A bad pair of headphones or, as I used, a speaker cable ending normal headphone jack $3.80
A tripod $0.00( already had one and isn't needed)
Recording device or computer with recording software

Step 2: Assembly

If you bought headphones, use the scissors to cut the actual headphone part off. We'll only need the cord for this so you can save the speakers for another project
Connect the photocell to the headphone's cables. Solder it or just tape it with electric tape.
That's it, really. It's that easy.

Step 3: How to Use

Using the tripod or other way to keep it steady, point the laser pointer at a window so that the reflection is in a spot that is not too difficult to reach. Now just position the photocell so that it's in the reflection. after doing that, connect the cord to the microphone plug-in and if you're using a computer, open your recording software. begin recording and it should pick up the sound.
Some tips:
If you want higher quality sound and less likelihood that people will see it, use a red laser to aim, then put an infrared laser( way too expensive for me and too hard to find) in it's place.
This project works best in dark places.
Curtains may help hide you but they muffle the sound quite a bit.

I had a sound file but there was a lot of light pollution in the room from an emergency light and the laser was being bounced off a clock's face which added a lot of background noise. I will upload a new sound file when i have a chance to make one.

Step 4: Thanks

Thanks for reading through my first instructable. If you liked it, please vote for it in the spy contest. Please don't try to use(or at least don't get caught using) this for anything illegal.



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    19 Discussions

    I just got in a 480mw IR laser to try one of these. Will be making a guide as I do It. I have worked with the real thing once before I retired form law enforcement. Aiming the IR lasers are the fun part. We used a digital video camera but your phones camera can see IR qlso.


    Reply 8 months ago

    Can you please elaborate on this point, Sir?


    1 year ago

    So im guessing nothing more came of this?

    Im not looking to tape a laser pointer to a tripod. That seems to be what your end result is.

    I shall try to compile and complete a better instructable than this one here.

    Hey! can you please give us more details on what wire to connect where? maybe a circuit diagram. We are in high school and this seems really hard.


    2 years ago

    There may be infrared pass filters that will filter out some of the more visible light . And let the infrared go through . Also I found that there is a lot of infrared in lasers . I found this out while reasearching Night Vission


    4 years ago

    its working with an led
    but wen i connected a speaker to the breadboard its not givin any reply


    5 years ago

    Also can I just plug the cord into a speaker so I can hear it ?

    1 reply

    Reply 5 years ago on Introduction

    In all honesty I am unsure. I had trouble when testing this and rushed to enter it in a contest. This instructable is practically unfinished and I have been meaning to remove it until I have had the time to fix it. Sorry for being unhelpful.


    5 years ago

    Please explain placement of the photocell . I'm new to this and want to build one but first I need to understand it.


    6 years ago on Introduction

    I am so anoyed at you for beating me to this idea, I was going to enter this but needed to order more photocencors.if you could better explane how this works you have a very big chance of winning.

    4 replies

    Reply 6 years ago on Introduction

    You might beat this if you find a way to make it ignore ambient light. (Hint: TV remotes do it.)

    One of the last steps already mentions infrared lasers. I just didn't have the time as I was going on a school trip and couldn't wait for the stuff to be shipped.


    Reply 6 years ago on Introduction

    Well thank you for the feedback. I knew someone else would have the idea so I kind of rushed it. I bought everything that day and did it all quickly. I am working on improving the instructions now so I hope that helps.

    Tanmay Das

    6 years ago on Step 4

    You can also use an infrared laser and receiver instead of ordinary laser.
    IR is invisible to the naked eye so you won't get caught and also any other outside light will not interfere with the receiver.

    1 reply
    bioboy725Tanmay Das

    Reply 6 years ago on Step 4

    I mentioned that at the end but I was rushing to get this up before anyone else could, so it was poorly worded.