Build a Laser Microphone Inspired by CIA Spy Systems (Film, 6m)
In the latest video from SomethingAboutScience, viewers get an intriguing look at the process of building a laser microphone, a device capable of eavesdropping on conversations from a significant distance using a laser beam reflected off a window. The author illustrates how sound waves impact the vibrations of the glass, allowing for the reconstruction of sounds occurring inside a room. The decision to use a visible red laser, rather than an invisible infrared laser typically used by professional spies, highlights a commitment to safety and transparency in this demonstration. It is important to note that this project is not intended for spying, but rather to showcase the technology at play.
The video delves deeper into the components necessary for creating a laser microphone. The author utilizes a photodiode, a sensor that converts light into an electrical signal, along with an amplifier circuit to boost the signal's strength. Working with these devices requires precision and a basic understanding of electronics. After extensive manual work, the author verifies the device's functionality by connecting it to a computer. Despite some challenges, sounds are detected, revealing the limitations of such a device—interference and background noise can obscure the clarity of the audio captured.
Undeterred, the author attempts to utilize two lasers to improve audio quality, but this only introduces more interference. Further efforts focus on stabilizing the laser microphone with a 3D-printed casing and incorporating polarizing filters to reduce ambient light interference. Reality sets in as, despite the efforts, achieving high-quality audio using a basic laser microphone proves difficult. This device may not seem practical for spying, yet there are agencies equipped with more advanced technology and budgets.
Laser microphones represent just one of many eavesdropping methods, prompting heightened security measures in government establishments. High-security buildings are often designed to thwart such technologies, and some facilities are even enveloped in Faraday cages to prevent signal interception. However, as the author points out, modern spying increasingly relies on hacking, transitioning traditional eavesdropping methods like laser microphones into the realm of advanced technology.
As stated by SomethingAboutScience, the video has currently garnered 929431 views and 41933 likes, reflecting a substantial interest in the topic. The content strongly engages viewers, showcasing a unique blend of science and technology in practical applications. Ultimately, the video not only educates but also stimulates the imagination, inviting viewers on a fascinating journey through the intersections of engineering and espionage.
Toggle timeline summary
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Introduction to the concept of eavesdropping using a laser microphone.
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Explanation of how laser microphones are used for surveillance.
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Basic mechanics of how a laser microphone works using reflections.
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Description of essential components needed, particularly a photodiode.
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Discussion about assembling and testing the laser microphone components.
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Testing the device's capability by simulating sound through a window.
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Demonstration of the audio results and background noise issues.
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Exploration of using two lasers to improve sound quality.
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Enhancements made to the device design for stability and functionality.
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Real-world applicability of laser microphones for government surveillance.
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Countermeasures against laser microphones in secure buildings.
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Conclusion on the changing landscape of surveillance techniques.
Transcription
Have you ever wanted to eavesdrop 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'd 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 they'd be more concerned about the explosives. The next thing you'll need is a photodiode. 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 ComiMark photodiodes 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 photodiode. The ones I bought came with a built-in microphone, so I had to remove that for the photodiode 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 aux 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 isn't even a laptop. It's just a piece of trash that can't seem to handle a mono-aux 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 photodiode. That way, when the beam oscillates, the photodiode 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 in 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. 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 at the same time, which would be a lot of static. So I decided to use two lasers to simulate the same situation. I placed my phone in the box while it played some copyright-free music at full blast. 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 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 installed 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. 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 to government agencies and law enforcement. Laser microphones are actually such a big problem that some high-security 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 eavesdropping 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.