Distant Eavesdropper

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new6ton
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Last night I watched the Purge Season 2. It was so unique becuase it is about events in inbetween the Purge Night.

I saw a part where the lady was eavesdropping on a conversation using this device she put on a table edge at a coffee shop.

purge eavesdropper.JPG


Is there eavesdropper device like it? Is it real? What are the official eavesdropper gadgets around and the most sensitive? When I googled "eavesdropper", I got only electronics products that you hide in room. I'm talking of a device that you carry that you can amplify the sound in certain directions.
 

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berkeman
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Is there eavesdropper device like it? Is it real?
It's TV, so who knows. Kind of looks like a telescope type optical instrument from the picture, so if you can read lips... :smile:

What are the official eavesdropper gadgets around and the most sensitive?
Well, there is the typical parabolic sound amplifier, but it's not very stealthy, and doesn't work if the folks you're snooping on are on the other side of a window...

https://i.pinimg.com/originals/49/e9/21/49e92104dcb7ee073b6e2fabe121018b.jpg
1572563839613.png


If there is a window in front of (or behind) the conversation, then the traditional device is an infrared laser reflecting off of the glass and an IR telescope to pick up the reflection. The small movement of the glass with the conversation can be converted into the audio conversation. I'll leave the details of that to the reader (you)... :smile:
 
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jrmichler
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Back in the 1970's, I was hanging around an airport where there was a movie shoot in process. The sound man had a portable tape recorder that was a little smaller than a typical briefcase. The microphone was about a foot long and an inch diameter with a foam cover.

I asked him how well that setup worked. There was an airplane doing an engine runnup right behind us, so I had to yell to be heard. He handed me the headphones and microphone. The headphones kept out the engine noise, and the microphone picked up a conversation between two people over 100 feet away. They were talking at a normal conversational level, and I heard them as clear as if I had been standing right there, and without any engine noise coming through.

And then I read about something called a shotgun microphone that was several feet long and several inches diameter.
 
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Could be a laser mic or a Phonak roger directional mic.
 
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What are the official eavesdropper gadgets around and the most sensitive?
1572571691906.png
 
256bits
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Not sure if this is the device - did it have a laser.

A window will vibrate from sound.
A laser can be used to obtain the vibrations from the window, and eavesdrop on a conversation of people within room in another building.
 
tech99
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I think the long stick type directional microphones are an end-fire array, like a TV antenna. Maybe a row of holes along a tube. But all these devices are best at higher frequencies, because even 1kHz is 30cm wavelength.
My friend was working near the focus of a 10m diamater radio dish and heard people speaking about 400m away.
 
new6ton
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What brand and model is the most sensitive in the world? I plan to buy one just to test how good it is.

https://www.ebay.com/c/600083263
this is an example of many out there but I'm not sure of the quality:

parabolic sound amplifer.jpg
 
berkeman
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What brand and model is the most sensitive in the world?
Not that little biddy one, that's for sure.

Quiz question -- why?
 
new6ton
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Not that little biddy one, that's for sure.

Quiz question -- why?
I think it's like a telescope. The bigger aperture, the better. I once had an 8 inches SCT telescope and a 4 inches. I wish I had a 12 inches SCT.

What is the biggest aperture sound amplifier available commercially and available to public? But if the amplifier is high quality and can eliminate noises. I guess it counts a lot too.
 
tech99
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The lowest frequency for telephone quality speech is 300Hz, which has a wavelength of about 1m. So how is a parabolic reflector about 200mm diameter going to do anything?? Why does it have holes in it, is there a profound reason?
 
new6ton
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The lowest frequency for telephone quality speech is 300Hz, which has a wavelength of about 1m. So how is a parabolic reflector about 200mm diameter going to do anything?? Why does it have holes in it, is there a profound reason?
I'll have only a one time shot to buy a 1 meter sound amplifier, for research or study purposes. If I buy a bad quality. I can't buy a second one (no budget). So has anyone seen or known the best brand of 1 meter sound amplifier out there? What brand is the one (pictured) shown in message number #2?
 
tech99
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The lowest frequency for telephone quality speech is 300Hz, which has a wavelength of about 1m. So how is a parabolic reflector about 200mm diameter going to do anything?? Why does it have holes in it, is there a profound reason?
In the case of an ear trumpet, part of the effect is the matching improvement between the impedances of the air and the ear drum. But I am not sure if a parabolic reflector will help the matching problem.
 
new6ton
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berkeman
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Say, can police used this on cars to get vibration of the windows and hear what you are talking or swearing about?
Of course. But in the US, they would need to get a warrant, which would normally mean that they would need to have evidence of bad things you were doing right now, like dealing drugs, etc. Is there something you would like to tell us?

But found it was so expensive, $14,500!
I can sell you a system for 13.5k. Just PM me your credit card information and we'll make it happen...
 
new6ton
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Of course. But in the US, they would need to get a warrant, which would normally mean that they would need to have evidence of bad things you were doing right now, like dealing drugs, etc. Is there something you would like to tell us?
I mean, some cars look suspicious. I haven't seen any movie where the police pointed a laser microphone at the windows of the car and listen to their conversations. Won't this be affected by other passing cars? Why would the window only vibrate to the conversations within? I have no particular use. Just out of curiosity. Just like I acquired a thermal imager for fun. In Fast and Furious Hobbs and Shaw. they use normal thermal imager (with FLIR brand) to look through a door. Very stupid scene, has anyone remembered it?

Also what is the divergent of the beam of this laser microphone? If it can harm a person a mile away. Then I'd keep out of it as it's dangerous.

Is there any radio device that can detect the presence of people in a room? This would be handy for some use or hobby.

Anyway. I read this: https://www.extremetech.com/extreme/187654-mit-can-now-eavesdrop-through-soundproof-glass-by-watching-the-vibrations-of-a-bag-of-chips


I can sell you a system for 13.5k. Just PM me your credit card information and we'll make it happen...
 
OCR
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Just like I acquired a thermal imager for fun.

Ah, so it was you. . . . 😒

Minnesota  Wind.gif


.
 
new6ton
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Ah, so it was you. . . . 😒

View attachment 252301

.
My only useful application for it was detecting ceiling with wetness above it from leak in roof that can't be seen from below.

ceiling thermal.jpg


It's rectangular plywood ceiling attached on long wooden bars. You can see the wooden bar as long shadowed. The very violet is more water than the lighter violet. You can't see the water yet from below because it hasn't leak yet. Too bad the resolution is only 140x140 pixels. I should have acquaired 640x640 for use outdoor in the forest to detect animals (but I don't camp anyway).
 
.Scott
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If you are interested, here is a report on a DYI project that created a laser interferometer microphone:
https://www.princeton.edu/~romalis/PHYS210/Microphone/index.html
In includes a few sound clips taken from the device. I'm pretty sure that the recurring tones are a resonant frequency of the window they are using. Any useful object is going to act like a drum head - and add some of its own tone to the sound.
 

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