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TM-106
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 TMS 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 MfS (Stasi) as TRM-106 [B]. 1

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.
  
Placing the radio bug inside the handset

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 Dutch T65.
  
The microphone of a vintage W48 handset

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 effective concealment, its high build quality and the fact that it was only on the air during a telephone call, the device was difficult to detect and discover. 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 [4].

  1. Note that this product was sold by many spy & security shops, under different model numbers.

Phone mike bug in the original storage box
Rear view of the phone mike bug
Close-up of the phone mike bug (note the frequency adjustment at 10 o'clock)
Phone mike bug aside a normal microphone
Standard Dutch T65-TDK telephone of 1979
Placing the radio bug inside the handset
German W48 phone from the 1950s
The microphone of a vintage W48 handset
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Phone mike bug in the original storage box
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Rear view of the phone mike bug
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Close-up of the phone mike bug (note the frequency adjustment at 10 o'clock)
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Phone mike bug aside a normal microphone
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Standard Dutch T65-TDK telephone of 1979
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Placing the radio bug inside the handset
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German W48 phone from the 1950s
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The microphone of a vintage W48 handset

Documentation
  1. TMS 'electronics' catalogue
    Date unknown, but probably early 1972/73. 1

  2. Telefon-Sprechkapsel-Sender TRM 106
    MfS, HA-III, Nr. 10592, page A1.2. 2
  1. Document kindly supplied by Detlev Vreisleben [2].
  2. Document obtained from BStU [3].

References
  1. Crypto Museum, TM-106
    Date unknown. Inventory number CM300497.

  2. Detlev Vreisleben, TMS electronic catalogue
    Received May 2019.

  3. Bundesbeauftragte für die Stasi-Unterlagen (BStU) 1
    Federal Commissioner for the Stasi-Records.

  4. Günter Wahl, UKW-Microspion in der Telefonkapsel (große Reichweite)
    ISBN 3-7724-0276-3. Microspione, 1977. Page 28-30.
  1. Full name: Bundesbeauftragte für die Unterlagen des Staatssicherheitsdienstes der ehemaligen Deutschen Demokratischen Republik (DDR) — 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.
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