Detect sound behind wall/door

You mean like putting a glass against the wall and your ear against the glass?

No, not possible.

It is only not possible if you can prove that it is not possible. No proof means it is still possible.

Remember the US cosulate in Moscow, Russia. The Russians pumped in microwaves thru the phone line. And the had a special transponder built into the United States Seal that they gave the consulate as a gift. The Russians heard everything that was said in the room, that the transponder was in.

Not possible, pshaw.

Yes.

On Sun, 25 Sep 2005 08:13:20 -0700, Don Lancaster wroth:

The correct answer is, "That depends."

To illustrate, you're on one side of the wall with a glass against the wall and your ear against the glass and I'm on the other side of the wall with a sledge hammer.

Jim

I read in sci.electronics.design that eeh wrote (in ) about 'Detect sound behind wall/door', on Sun, 25 Sep 2005:

It depends how loud the sound is, obviously. If the microphone is in direct and intimate contact with the wall, the sensitivity will be very much higher than if it isn't.

rubbish, Don, see this graph

martin

Think about this: There might be noise outside the room, which would overwhelm any sound from inside, no matter how sensitive or powerful an amplifier you use. Because the sound coming through the wall from inside the room will be extremely weak, any little vibration or noise would totally obliterate it. You need to have a very quiet room to place your detector in.

Through the door would work better, just because the signal from inside the room is less attenuated.

Now get away from my door.

Microwave through a phone line?

I read in sci.electronics.design that Michael A. Terrell wrote (in ) about 'Detect sound behind wall/door', on Sun, 25 Sep 2005:

Hollow wires.(;-)

Microwaves through twisted pair. Neat!

I do believe the bugs in question were the precursor to RFID. They only responded to (massive, BTW) microwave radiation and were dormant otherwise. They did much the same thing to the "new" US Embassy in Moscow. You know, the one that was never occupied. Telephone lines, pshaw!

Can you be more specific? I imagine that under some circumstances it would be possible.

Are you trying to determine the feasibility of some kind of high-tech eavesdropping device?

I know in the movie _Clear and Present Danger_ some kind of laser interferometry microphone was shown being used. Don't know if that works in real life, particularly on a concrete wall.

If it does work, then RF interferometry might work, too.

--Mac

Can you open the door?

I remember hearing/reading the 'bugs' were resonant cavities in all the cast concrete beams courtesy of the local Russian contractors. So all the walls were transmitters when a nice beefy beam was pointed at it. The resonance was modulated by air pressure across the cavity. Similar trick to bounce a laser off a window that is being vibrated by speech and demodulate the return. Countermeasure is to play the radio real loud in the room.

The US also imported some "cone of silence" rooms that could be installed inside the compromised embassy buildings, complete with sound muffling and Tempest-quality electronics interfaces.

Or using an electronic stethoscope?

David

D> eeh wrote:

Nope, too much phase shift.

Hi--- If the music on the radio is identifiable, then it can be nulled out by using the same music to null out the mish-mash (on the recording). If it's a radio station, the same should apply. The resultant will be the conversation that took place.

Best--- Ron

On 28 Sep 2005 18:27:30 -0700, Winfield Hill wroth:

Feet of clay... feet of clay...

I used to consider you my idol, but I think you're simply wrong this time. A tracking filter with a bandwidth of a few 10's of Hz derived from the interfering audio source should ignore phase shift. The signal may have to be run through the filter several times, but the original conversation should finally emerge.

The fact that conversation contains a great deal of redundant information makes it possible.

Jim

I read in sci.electronics.design that snipped-for-privacy@nowhere.net wrote (in ) about 'Detect sound behind wall/door', on Thu, 29 Sep 2005:

The mind boggles!