Laser microphones have been around since the Cold War. Back in those days, they were a favorite tool of the KGB – allowing spies to listen in on what was being said in a room from a safe distance. This project by [SomethingAbtScience] resurrects that concept with a DIY build that any hacker worth their soldering iron can whip up on a modest budget. And let’s face it, few things are cooler than turning a distant window into a microphone.
At its core this hack shines a laser on a window, detects the reflected light, and picks up subtle vibrations caused by conversations inside the room. [SomethingAbtScience] uses an ordinary red laser (visible, because YouTube rules) and repurposes an amplifier circuit ripped from an old mic, swapping the capsule for a photodiode. The build is elegant in its simplicity, but what really makes it shine is the attention to detail: adding a polarizing filter to cut ambient noise and 3D printing a stabilized sensor mount. The output is still a bit noisy, but with some fine tuning – and perhaps a second sensor for differential analysis – there’s potential for crystal-clear audio reconstruction. Just don’t expect it to pass MI6 quality control.
While you probably won’t be spying on diplomats anytime soon, this project is a fascinating glimpse into a bygone era of physical surveillance. It’s also a reminder of how much can be accomplished with a laser pointer, some ingenuity, and the curiosity to see how far a signal can travel.
Interresting hack
The background noise looks like white noise or so.
It could be coming from the sensor itself or from the preamplifier.
According to the documents, it appears that the Russians used the infrared beam initially.
Nice tech, in hindsight i can add this as an extra reason why i outfitted my house with triple glass insulation ;)
Nice, now try this in Europe, where everyone has Double+ glass insulation windows.
Ever held a light source in front of a double insulated window? The second element reflects as well. In fact double+ insulation works even better. Unfortunately OP didn’t go any further. The heard noise in this example comes from the input amplifiers. You really need an LNA. Also best results will come from using a line generating optic like that from a line laser behind a collimating lens at the receiver end. What you will notice in a real world example is that environmental noise, like street noise, will interfere and drown your signal beeing interested. Now the funny thing is: The first glass element will dampen the street noise. The second glass element (inside) will carry a much better signal as the noise from the street is being attenuated. So you just have to go for the second reflection.
This video is muted on so many levels, it’s sad we don’t have free speech anymore.
“You have the right to free speech… as long as you’re not dumb enough to actually try it!”
~The Clash, “Know Your Rights”
Disclaimer: I’ve not watched the video and am not sure what you mean exactly (what is “muted”?).
A) Free speech doesn’t mean consequent free speech.
B) Private platforms (YT/TwiXXer/FB/…) not allowing your stuff has nothing to do with free speech. Can you be thrown out of any church (christian, muslim, jewish, etc.) for spouting nazi paroles, anti-semitism and whatnot? Can a LGBTQ+ friendly bar owner throw you out when you’re a bigot? …
When “talking” about stuff is forbidden by law, THAT is a reduction of free speech.
But even then the context may be relevant: AFAIK In Germany you’re free to use forbidden symbols like the swastika and whatnot in (academic) discussions/discourse (=free speech); but not “just like that” in public on eg. clothes, signs and so forth (=’propaganda-ish’).
Yes, it’s not clear cut and a tight rope to walk on but it is still a lot better than some people (politicians!) complaining about being “silenced” because FB and the like (shadow) banned them.
Thank you [limroh]! This needs to be shouted from the rooftops.
A) That’s true but there is some nuance in what could be considered fair consequences.
B) I don’t know if this is entirely true anymore, or at least there is some reasons to debate this idea. As it stands, social media has taken on almost the entirety of public speech. If allowed to manipulate it as they wish, corporations can silence opinions and manipulate public discourse to an unsettling degree.
Politicians on social media have already had some strange interactions with the legal system like the courts basically banning them from blocking people. I would be concerned if platforms could just ban politicians whenever they feel like without some really good justification, so far they’ve been hesitant to abuse that ability because of how much attention and controversy that’d draw. IIRC they’ve only done it a few times, generally when it’s pretty extreme, and even then it still drew a lot of attention and discussion.
Really the point is about balancing rights i.e. your right to swing your fists ends at (near) someone’s face. One person or corporations rights can’t be allowed to trample on other’s. Also there is some arguments on how many rights corporations should have because there have been some crazy cases of them having (very likely) too many rights to a point where they can get away with things they shouldn’t.
It would greatly aid in deployment if there were an optical guide for aiming. An inexpensive rifle scope would do the trick, and a more “longitudinal” form factor to facilitate this.
Um, you need to see the reflection of the laser. If the target window is on the 3rd floor , you’re going to have to catch the reflection on the 6th floor of an adjacent building, assuming there is one. It’s not too hard to find a visible red beam’s reflection, but an IR beam is going to be a lot harder. Sure, it could work under just the right circumstances, but it will take some serious effort to ensure that the reflected beam is where you can find it and access it.
How does the IR thermometer work then if it doesn’t need retroreflection?
The visible laser in IR thermometers is just there so you know what the thing is pointed at. The laser has nothing to do with reading temperature.
“retroreflection” aha. Like advancing backwards in a straight curve ?
You could just go up to the third floor of the adjacent building. Then you could catch the reflection from the same height.
Third attempt… Assuming there was an adjacent building at the right height, assuming you had access to the right windows (not necessarily on the same floor) for the laser and receiver in that building, assuming the buildings are close together, and assuming their windows are close to parallel. That’s a LOT of assumptions…
Except none of that is true. In the video you can see he doesn’t have the laser directly in line with the window. And this exact technique has been used successfully in the past by government agencies. Windows are not perfect mirrors, some of the reflected light is going in all directions. You just need to catch enough of it to get the signal you need.
It… Literally works. Without all these assumptions you speak of.
Heck, When you think about it you want to be off-normal. That way deflection will move the beam on and off the receiver.
IR was used because at that time nobody could see it, but expensive/rare sensors could. Now everyone can.
With current equipment all you have to do is remove the IR filter from your digital camera and you can see an IR beam pretty well – cheap webcams are great for this. Or you could use your phone camera as-is (which is how you check if an IR remote is sending commands to your TV) since they retain their IR sensitivity. A row of IR emitters under the brim of a hat has been a way to foil facial recognition for some time.
So, since the phone camera gambit works so well, if you’re surveilling something in public, not only the reflected beam but the emitter source will be visible in every selfie and security camera in the area. Probably a moment of fame you wouldn’t want.
No!
1. It is not “easy” to remove an IR-filter of a camera as almost every camera comes with a IR-filter substrate ontop of the bayer filter.
2. The only reason you can see some of the IR-LEDs is because they emit a broader spectrum that can partially pass the filter. A real IR-laser is almost at single wavelength and is totally invisible to camera IR filters.
As I posted separately: Forget about seeing all infrared light just with a modded camera or phone. Those only see near infrared in 700 to 1000nm. Even good wide black and white sensor hardly work past 1000nm, and don’t past 1100nm. Even Gen3 Nightvision is pretty useless for 950nm and above, and digital nightvision and use IR illuminators at 850nm, but works if stronger at 880nm and LEDs at 940nm. You don’t see 980nm laser illuminators even though 200mW is very cheap. Because they hardly work. At night in dark. Good luck seeing that light during daytime if there is other more visible light nearby. You need a special SWIR camera to see past 1100nm, and those are not cheap or common. 1300-1500nm lasers and sensors can be very cheap.
For this simple type to work, yes you need to catch the bounce. But with some better optical setup, especially the receiver, you can use any reflection where vibrations will change how your sensor see the reflected light and it might be enough to use polarisation to go through the window, and hit a fairly dull surface that change the scatter, and use an narrow band filter so the sensor only see the lasers light, muting other light noise in the signal received, and modulate the laser with a carrier wave, and then filter the sound through that frequency. Like he said, a picture on the wall, a slightly dirty mirror or other inside glass surface, or decorative artwork and such with a curved shape, can work better than the window, and since the human eye can’t see infrared, we don’t really know how items look or reflect in other light spectrums. You might be able to bounce light and get a corner reflection on something else. You might even use smoke, which has been demonstrated. And forget about seeing all infrared light just with a modded camera, those only see near infrared, and even good wide black and white sensor hardly work past 1000nm, and don’t past 1100nm. 1300-1500nm lasers and sensors can be very cheap. They’re used in fibre optics and other tech.
Personally, I much prefer:
https://hackaday.com/2015/12/08/theremins-bug/
Using a remote element for RF right under everyone’s nose.
You are right, see my note below. I’d forgotten about the Theremin connection; there was a resonant chamber built into the Great Seal of the United States which was “gifted” to the embassy by a group of “schoolchildren”.
IIRC currectly the Russians used microwaves in the 1950s version of this against the U.S. Diplomatic facility in Moscow.