Wireless telephone element
TM-106 was a wireless
covert listening device (bug) in shape of a
standard telephone element, supplied in the early 1970s by
in Köln (Germany) and, under different names,
by several spy and security shops in Europe, including
the PSS Spy Shop
in Amsterdam (Netherlands).
As it was an illegal device — it contains a transmitter —
it was sold 'under the counter' and was advertised
'for export only'.
During the Cold War
the device was known by the
Back in the 1980s, in the days when the national telephone companies (the PTT) had
not yet been privitized, most (if not all) handsets of domestic telehone sets
contained similar microphones and speakers. When the carbon microphone of an old
telephone was broken (which happened rather often),
it could easily be swapped for a new one by unscrewing
the mouth-piece of the handset.
The radio bug shown in the image on the right is built inside the casing
of a standard microphone element, making it virtually indistinguishable
from an original microphone used in those days.
As all telephone sets of the 1950s through to the mid-1980s used a carbon-based
microphone element, the phone had to provide a DC bias voltage of 8 to 10
Volt for the microphone. When small electret microphones (with built-in
amplifiers) and transmitters became available during the 1980s,
it became relatively easy to exploit
this voltage to power a miniature radio transmitter.
The device shown here works in the 100 MHz FM band and has a small screw,
hidden behind one of the circular holes,
to adjust the frequency. It has an operational range of 25 to 50 metres.
One of the great things of the analogue era, is that virtually all telephone
handsets, regardless manufacturer or country, had a microphone with the same
form factor. As a result, the bug could be used anywhere in the world.
The image on the right shows the bug with a typical German W48 telephone
of the 1950s, wheresas in the image above it is used with a later
Bugs of this type are easily installed in an existing telephone without
any technical knowledge or skill.
They were therefore frequently used
for industrial and private espionage during the 1980s and 1990s.
A standard domestic FM receiver in a nearby room was enough to eavesdrop on
a conversion. The transmitter was switched on automatically
when the user picked up the handset. The user would not notice the presence
of the transmitter as the device would act like a normal microphone.
Due to leakage, the transmitter would pick-up
both sides of the conversation.
The TM-106 can bee seen as a semi-professional radio bug. Due to its
its high build quality and the fact that it was only on the
air during a telephone call, the device was difficult to detect
It was also sold as a test transmitter with professional bug tracing
equipment, such as the
Audiotel Scanlock ECM,
and was used to train bug-sweeping teams.
A similar capsule bug was described in 1977 by Günter Wahl
in his excellent book Microspione .
Note that this product was sold by many spy & security shops,
under different model numbers.
Document kindly supplied by Detlev Vreisleben .
Document obtained from BStU .
Full name: Bundesbeauftragte für die Unterlagen des Staatssicherheitsdienstes
der ehemaligen Deutschen Demokratischen Republik
Federal Commissioner for the Records of the
State Security Service
of the former German Democratic Republic (GDR) —
officially abbreviated to BStU.
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© Crypto Museum. Created: Monday 29 April 2013. Last changed: Saturday, 06 June 2020 - 10:10 CET.