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Snooping Through Walls with Microwaves
denis-The-menace writes "According to an article from newscientist, scientists have devised a system to use microwave energy for surveillance. If people are speaking inside the room, any flimsy surface, such as clothing, will be vibrating. This modulates the radio beam reflected from the surface. Although the radio reflection that passes back through the wall is extremely faint, the kind of electronic extraction and signal cleaning tricks used by NASA to decode signals in space can be used to extract speech. Although, I doubt it would work in this room"
How many criminals protect against laser audio surveillance, where a laser beam is bounced off a window or other rigid surface, and the sound from the room vibrates the surface, wobbling the beam, the wobble being translated into audio by the snooper.
The laser can be defeated by double glazing (I think), devices to vibrate windows and laser detectors (to tell you if you're being listened to).
A microwave device can be defeated by the good old tinfoil hat - by which I mean wallpapering in foil or otherwise turning the room into a faraday cage.
- There were no "lasers" in 1960. At least not the very stable continuous-wave lasers that you need for this, and especially not in the USSR.
- Think-- do lasers go through glass? Do lasers bounce off glass? Might other wavelengths of electromagnetic radiation act similarly?
- Microwaves bounce off most anything, if you pick the right angle. Conveniently, most buildings have the windows recessed a bit, and any concave corner makes an EXCELLENT "corner reflector", which has the amazing property of bouncing any incident beam right back to the sender.
Not only did they bounce microwaves off glass-- they had the hutzpah to give the US ambassador a honorary plaque, which he hung on his office wall. Unbeknownst to us, there was a little diaphragm inside the plaque, just the right wavelength to reflect K-band microwavesm, which vibrated very nicely to every word spoken in his office. Look it up.MI5 developed this in the 1950s, and called it Special Facilities. All it required at the start was a modification to the phone - a single washer, and the phone could be used as a surveillence device. Later versions enabled activation using high frequency radio waves to activate the telephones microphone and required no modification to the phone itself.
Survellience was also carried out against embassy cypher machines using unshielded telephone cables picking up eletromagnetic emissions from the cypher machines, in many cases enabling the reading of both the en clair message and the cypher material.
None of this was admissable in a UK court. Phone tap evidence still isnt.
There's an anecdote in the engineering field: where some poor sods at Racal-Dana had a phase detector at 50MHz that was so sensitive to vibration they had to stop their experiments whenever a plane took off from Orange County Airport (quite a few miles away). They eventually had to get special thick aluminum wall castings to enclose the phase detector to block the vibrations. And this was at just 50MHz. Phase detectors get more sensitive proportional to operating frequency, so a 5,000 MHz phase detector is *mighty* sensitive!
The first sign the Fed's are listening to you is when they give you a nice small bust of lenin for your mantle peice. That's exactly what the British did to the russian ambassador back in the post world-war two era. They gave him a a gift of a small statue and inside it they had mounted a corner cube which is a passive device that enhances the retro-reflection of microwaves beamed at it. (read about it is Peter Wright's (banned in UK) book Spycatcher--wright was the science officer for MI5 and inventor of the technique)
The second sign is when you feel toasty warm and the chair feels cold. In the 70's and 80's the carter and reagan administrations were perpetually complaining that the level of microwave energy measured inside the US embassy exceeded the OSHA limits for exposure. Eventually the US built a new embassy with enhanced shielding. UNfortunately the Soviet's put listening devices into the bricks. The embassy had to be knocked down and rebuilt. Of course, peter wright did exactly the same thing to the Soviet embassy in canada. Each night he snuck into the construction site and pulled wires up the inside of the walls to his microphones in specially made window sills. The soviet's learned about it from a mole in MI5 and had to build a second interior wall so that no rooms were near the windows.
Doppler microwave spying is quite old. As is laser vibrometry on windows.
Some drink at the fountain of knowledge. Others just gargle.