I Built a CIA Spy Device (Laser Mic)

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00:00Have you ever wanted to eavesdrop on conversations happening in a room thousands of feet away using

00:04a laser? Of course you have, especially if you're a Soviet KGB spy during the Cold War era.

00:10Today I'll be making a laser microphone, a device now used by federal agencies like the CIA to spy

00:16on conversations when they don't want to risk planting a microphone inside of a room.

00:20A laser microphone can pretty much turn a window into a microphone from a long distance.

00:24It works by shining a laser beam at a window or a picture frame inside of a room and capturing

00:29the reflection of the beam with a sensor. Any conversations inside the room will send sound

00:34waves through the window, causing it to vibrate slightly. These vibrations of the window will

00:39modulate the reflected beam of light, and by capturing and processing those oscillations,

00:43we can reconstruct the sound waves and hear what's happening inside.

00:47Now for obvious reasons, if you're using this for spying, you'd want to use an invisible infrared

00:51laser. But for this video, I'll be using a visible red laser, so just to be clear YouTube, this is

00:56not a tutorial on how to spy on people. Though to be honest, I think they'd be more concerned

01:00about the explosives.

01:02The next thing you'll need is a photodiode. This is basically a mini solar cell that converts

01:07light into an electrical signal, except it's much more sensitive and has a faster response

01:11time. You can find these inside the receivers of most modern TVs and some smoke detectors,

01:16although these are usually designed to detect infrared light, so if you want to spy on people,

01:20this is what you want to use. But you can also find them on Amazon. These Commimark photodiodes

01:26will work great for detecting the red laser, plus the name fits the Soviet theme pretty well.

01:30Next, you'll need an amplifier circuit to boost the weak signal from the photodiode. The ones

01:36I bought came with a built-in microphone, so I had to remove that for the photodiode to take

01:40its place. Then I stripped the end off of a charger so I can power the circuit, and I did

01:44the same to an aux cable so I can output the signal to a laptop. And after covering everything

01:49with some hot glue to prevent any short circuits, the receiver is pretty much done. Now I just

01:54need to test it out by plugging it into a laptop.

01:58Okay, so it turns out this isn't even a laptop, it's just a piece of trash that can't seem

02:02to handle a mono aux cable. My only other option is my desktop computer, which unfortunately

02:07means the device won't be portable enough to spy on any government officials. But the good

02:12news is, my computer actually recognizes it as a microphone. But can it really pick up sound

02:17through a window? To find out, I positioned the laser to reflect off this piece of glass

02:21taped to the inside of a box, which will simulate a window. I had to carefully align the laser

02:26so its reflection landed precisely on the sensor across the room. For this to work, the reflection

02:31needs to be just off to the side of the photodiode. That way, when the beam oscillates, the photodiode

02:36receives varying amounts of light. If the beam were perfectly centered on the sensor, it would

02:41just keep outputting the same voltage, giving us no useful data. However, if the beam is wider

02:46than the sensor itself, it wouldn't really matter as much, since most lasers have a gradient

02:50of intensity, so as the beam oscillates, the sensor still detects fluctuations in light levels.

02:55To simulate a voice behind the window, I placed my phone in the box while it played some copyright-free

03:00music at full blast. And here's what my computer received from the sensor.

03:30As you can hear, the audio is actually distinguishable, but there's still a lot of

03:39static in the background. Not only does the window vibrate, but any vibrations of the laser

03:44or the receiver will be picked up as well. I can't get rid of the static completely, but instead of

03:49using one laser, you could reflect two lasers off the window and capture their reflections on two

03:53separate sensors. And by comparing the two different waveforms, you can cut out anything that

03:57doesn't match between the two to get rid of some of the noise. But since I'm definitely not doing all

04:02that, the best I could do is make the laser and receiver more stable. So I 3D printed this casing

04:07for the sensor for it to be easily mounted onto a base or a tripod. To make powering it more

04:11convenient, I added this power inlet, and since ambient light can be a problem, I included an

04:16adjustable polarizing filter, which will block out some ambient light while still letting the laser

04:20through. And after all that, it still sounds like crap.

04:50Now, this device may seem impractical for real surveillance, but keep in mind, the government

05:12has a much larger budget than $30, and they definitely still use this technology for surveillance.

05:17Just look at this company. They sell 10 different versions of this thing, and they only sell the

05:21government agencies and law enforcement. Laser microphones are actually such a big problem that

05:26some high-security government buildings are specifically designed to block them.

05:30The easiest countermeasure is to just not have confidential conversations near a window.

05:34But that's not always enough, because similar eavesdropping techniques exist using radio or

05:39microwave frequencies to detect sound vibrations from objects deep inside of a building.

05:43That's part of the reason some secure rooms or even entire buildings are wrapped in a Faraday cage

05:48to block all signals in and out. However, this form of spying is gradually being phased out,

05:53as modern surveillance increasingly relies on hacking phones and computers to intercept

05:57electronic communications.

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