Resonant cavity microphone
- wanted item
was a passive covert listening device (bug),
developed in the UK in 1953 by
at the Marconi Company, for the British intelligence agency
It was inspired on a novel Russian
covert listening device known as
that had been found in 1952 hidden inside the Great Seal
of the United States, that hung in the Ambassador's study
at the residency in Moscow.
Immediately after the discovery of
The Thing, it was flown to
Washington (US) and handed over to the FBI,
where it was examined at the FBI's
On 1 December 1952, the FBI released
a technical description of it, along with photographs
and detailed drawings .
In his book Spycatcher ,
Peter Wright suggests that the Americans
had no idea how the device worked – hence the name
The Thing –
and that they turned to the UK for help, where he (Wright) solved the
mystery in 10 weeks time for MI5.
It turned out to be a resonant cavity microphone.
It is uncertain whether Wright's account is correct however, as it has
since become clear from FBI documents that were released in 2014 and 2015,
that Wright wasn't the only one trying to solve The Thing's mystery.
It is known that the FBI, the SCEL and the CIA had all been
running their own research
and had all created a series of working replicas,
one of which was given to Wright.
It is possible that Wright wasn't presented the full picture by MI5
and the American FBI at the time.
In any case, Wright understood the principle behind the device
and grasped its potential. At the time (1952) he was still employed as
a Navy Scientist, attached to the Marconi Company, where he worked on
antisubmarine Radar. After completing his research on the Russian resonant
cavity microphone for the Americans, he was asked by
MI5 to develop a British variant of it.
After arranging the necessary funding, something that was quite difficult
in the days when MI5 officially didn't exist, Wright was assigned a
suitable laboratory at the Marconi premises and took off.
Approximately 18 months later the new device, that had been codenamed
SATYR was ready. It came with a suitcase filled with equipment,
and two aerials that were disguised as ordinary British umbrellas.
When unfolded, the umbrellas were used as transmitter and receiver dishes .
With the device ready for its first demonstration,
Wright and his colleague Kemp, went up to the MI5 headquarters at
Leconfield House in Curzon Street, London, and showed it to Deputy Director
Roger Hollis. The umbrellas were set up in Hollis' office, whilst
SATYR was placed in an MI5 flat just around the corner on South Audley Street.
According to Wright's own account, the device worked perfectly and had a very
good audio sensitivity. It was able to pick up any sound in the room, from (test)
speech to the turn of the key in the door.
Hollis called it Black Magic .
After the successful demonstration, SATYR was taken into production
and was used in covert operations by the British, Americans,
Canadians and Australians.
It became one of the best methods for covert eavesdropping during
the 1950s, until it was succeeded by new equipment.
According to Wright, the Americans 1 ordered twelve sets and cheekily
copied the drawings and made twenty more.
The whole SATYR operation had great consequences as it established
Wright's credentials as a scientist with MI5. In 1954 he would become
MI5's first Principal Science Officer.
Here Wright probably refers to the CIA
and their project EASYCHAIR.
It seems likely however, that the CIA was not aware of Wright's activities
at all, as MI5's (and hence Wright's) contact with the Americans on the
subject of the Russian resonant cavity microphone, ran via the FBI
and not the CIA.
It is known that the FBI ordered some British devices for evaluation
in 1953 .
This is further supported by David Wise in , where
he writes ...unknown to Karlow and the CIA, British Intelligence had
succeeded in replicating the Soviet bug, which MI5, the British internal
security service, code-named SATYR.
No further information is currently available.
As far as we know, there are no surviving SATYR devices and there are
no images of it in the public domain. Please help us expand this page.
If you have any additional information, photographs, drawings or equipment,
please contact us.
Although it is by no means certain, there are indications that the device
had a resonance frequency of 1400 MHz, which whould have been the illumination
It is likely that – like the
Russian original –
it re-emitted the illumination frequency.
According to Peter Wright,
SATYR was successfully used by a number of intelligence services
of the English-speaking countries throughout the 1950s, but unfortunately
we do not have access to any surviving stories to illustrate this. In his
book Spycatcher [1 p.83], Wright gives examples of bugging
operations that technically succeeded, but that produced
no useful intelligence.
In 1957, Wright went to Montreal (Canada) to assist the
RCMP with the
installation of two SATYR devices in one of the walls of the future
Polish Embassy. Soon after their installation however, the Poles ordered
the constructor to remove the wall and replace it by another one.
The RCPM later learned from an informant
that the Poles had been tipped off by the Russians.
➤ More about Peter Wright
A similar thing happened in Australia two years later, in 1959.
The Russians, who had broken off their diplomatic relations with Australia
after the Petrov Affair in 1954 , were making plans to return.
The Australian intelligence service ASIO,
wanted to mount a bugging
operation against them, and Wright advised them to use a SATYR device,
mounted in the wooden frame of one of the windows. One of Wright's
assistents went to Australia to help the ASIO installing the device.
As Wright assumed the Russians to be monitoring the building for microwaves
right after their return, he instructed the ASIO to leave the device off
during the first months of reoccupation. When the device was finally
activated, every sound in the room could be picked up, from the shuffling
of papers to the scratch of a pen, but not a single word was ever spoken...
Although Wright has always assumed that the Russians had been tipped off by
a mole in one of the Western intelligence services,
which was probably the case,
they had also developed their own technical countermeasures against
resonant cavity microphones. After all they were the first to use the
technology themselves and had
used it against the US Embassy in Moscow
for 7 years.
An example of a Russian countermeasures receiver that was developed especially
for the detection of resonant cavity microphones, is the OSOBNJAK 8 shown in
the image on the right.
The device is housed in an unobtrusive briefcase and can detect strong nearby
RF signals between 100 MHz and 12 GHz; the signals that were typically used to
activate such microphones.
➤ More about Osobnjak 8
Partly released by the FBI under the Freedom of Information Act (FOIA)
on 3 September 2010.
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© Crypto Museum. Created: Tuesday 12 January 2016. Last changed: Saturday, 23 July 2022 - 10:08 CET.