have you ever wanted to e drop on conversations happening in a room thousands of feet away using a laser of course you have especially if you're a Soviet KGB spy during the Cold War era today I'll be making a laser microphone a device now used by federal agencies like the CIA to spy on conversations when they don't want to risk planting a microphone inside of a room a laser microphone can pretty much turn a window into a microphone from a long distance it works by shining a laser beam at a window or a picture frame inside of a room and capturing the reflection of the beam with a sensor any conversations inside the room will send sound waves through the window causing it to vibrate slightly these vibrations of the window will modulate the reflected beam of light and by capturing and processing those oscillations we can reconstruct the sound waves and hear what's happening inside now for obvious reasons if you're using this for spying you would want to use an invisible infrared laser but for this video I'll be using a visible red laser so just to be clear YouTube this is not a tutorial on how to spy on people though to be honest I think to be more concerned about the explosives the next thing you'll need is a photo diode this is basically a mini solar cell that converts light into an electrical signal except it's much more sensitive and has a faster response time you can find these inside the receivers of most modern TVs and some smoke detectors although these are usually designed to detect infrared light so if you want to spy on people this is what you want to use but you can also find them on Amazon these commi Mark photo DS will work great for detecting the red laser plus the name fits the Soviet theme pretty well next you'll need an amplifier circuit to boost the weak signal from the photo diode the ones I bought came with a built-in microphone so I had to remove that for the photo di to take its place then I stripped the end off of a charger so I can power the circuit and I did the same to an ox cable so I can output the signal to a laptop and after covering everything with some hot glue to prevent any short circuits the receiver is pretty much done now I just need to test it out by plugging it into a laptop okay so it turns out this is isn't even a laptop it's just a piece of trash that can't seem to handle a mono Ox cable my only other option is my desktop computer which unfortunately means the device won't be portable enough to spy on any government officials but the good news is my computer actually recognizes it as a microphone but can it really pick up sound through a window to find out I positioned the laser to reflect off this piece of glass taped to the inside of a box which will simulate a window I had to carefully align the laser so Its Reflection landed precisely on the sensor across the room for this to work the reflection needs to be just off to the side of the photo diode that way when the beam oscillates the photo diode receives varying amounts of light if the beam were perfectly centered on the sensor it would just keep outputting the same voltage giving us no useful data however if the beam is wider than the sensor itself it wouldn't really matter as much since most lasers have a gradient of intensity so as the beam oscillates the sensor still detects fluctuations and light levels to simulate a voice behind the window I placed my phone in the Box while it played some copyright free music at full blast and here's what my computer received from the sensor [Music] [Music] as you can hear the audio is actually distinguishable but there's still a lot of static in the background not only does the window vibrate but any vibrations of the laser or the receiver will be picked up as well I can't get rid of the static completely but instead of using one laser you could reflect two lasers off the window and capture the reflections on two separate sensors and by comparing the two different waveforms you can cut out anything that doesn't match between the two to get rid of some of the the noise but since I'm definitely not doing all that the best I could do is make the laser and receiver more stable so I 3D printed this casing for the sensor for it to be easily mounted onto a base or a tripod to make powering it more convenient I added this power Inlet and since ambient light can be a problem I included an adjustable polarizing filter which will block out some ambient light while still letting the laser through and after all that it still sounds like crap [Music] [Applause] [Music] [Applause] [Music] now this device may seem impractical for real surveillance but keep in mind the government has a much larger budget than $30 and they definitely still use this technology for surveillance just look at this company they sell 10 different versions of this thing and they only sell the government agencies and law enforcement laser microphones are actually such a big problem that some highsec government buildings are specifically designed to block them the easiest countermeasure is to just not have confidential conversations near a window but that's not always enough because similar Epping techniques exist using radio or microwave frequencies to detect Sound Vibrations from objects deep inside of a building that's part of the reason some secure rooms or even entire buildings are wrapped in a faraday cage to block all signals in and out however this form of spying is gradually being phased out as modern surveillance increasingly relies on hacking phones and computers to intercept electronic communications