Wireless contact microphone
TM-104 was a
covert listening device (bug)
with built-in contact microphone,
supplied in the early 1970s by TMS Electronic
in Köln (Germany). The miniature
transmitter worked in the FM radio broadcast band (90-110 MHz) and was intended
for listening through walls and windows.
The actual transmitter is housed in a black plastic enclosure that measures
58 x 38 x 18 mm and weights 50 grams. It is powered by three internal Mallory
button cells that last – depending on the – for up to 2600 hours.
The range of the device, under optimal conditions, is between 400 and 800
The device is attached to a metal bracket with two suction cups 1 that allow
it to be fitted to a window, using the glass as a membrane for the internal
contact microphone. According to the brochure, the microphone is very
The transmitter is enabled by
inserting a small shorting plug
into the 2.5 mm jack socket at the top.
This socket can also be used for connection
of a switching receiver, allowing the bug to be activated remotely.
At the other side of the device is the antenna socket, which accepts a
regular miniature banana plug
– such as the ones used with model railways –
with a 75 cm piece of wire.
The enclosure consists of two black plastic case shells, that are simply
pressed together. The two halfs can easily be separated, so that the battery
compartment can be accessed. The image on the right shows the interior of the
device, with the rectangular battery compartment at the centre.
The only component that is visible, is the white ceramic trimmer that is used
for adjusting the transmission frequency. The other electronic parts are all
cast in white artificial rubber. This was done to improve the stability,
but also to protect the circuit design from being copied.
Like all TMS transmitters,
the TM-104 operates by default in the FM radio
broadcast band, and can be adjusted to any frequency between 90 and 110 MHz,
allowing a regular domestic FM radio to be used for reception. This has the
disadvantage that the transmitter can also be picked up (accidentally) by
anyone who searches a station. For this reason, the transmitter could
also be ordered for frequencies in the 2 meter (150 MHz) or 4 meter (75 MHz)
band, but this required a special receiver, which was also available from
Note that neither of these transmitters could be operated legally
within Germany, so they were listed as 'Nur für export' (for export only)
These are regular domestic suction cups that are normally fitted to the
kitchen tiles, with a plastic hook for hanging the towel. The hinged
black hooks also function as a handle when fitting the cups.
According to the brochure [A], the TM-104 was available in two versions –
S and L – both of which were cast in white artificial rubber to make it
shock and tropical proof. In addition, both version could be ordered for
other frequency ranges as well.
- TM-104 S
This is the standard version of the device, that had a specified range of
approx. 800 metres. It was powered by three Mallory MN-625-G button cells,
which lasted for 40 hours, or by three RM-625-H for 120 hours of operation.
- TM-104 L
This is the long-duty variant with has a range of 400 metres.
When powered by a Mallory MN-1500 battery, it could transmit for 1500 hours,
and with an RM-502-H battery even as long as 2600 hours.
Apparently, the TM-104 was also used during the
Cold War by the
Statni Bezpecnost (StB) —
the repressive secret civil intelligence service
— as it is on public display at the
Police Museum in Prague as Štěnice x (bug x). 1
According to the note (in German) in front of the device, it was
remote-controlled by means of a switching receiver named SOVA. 2
This was done by connecting the switching receiver to the white mini-jack
at the top.
The photograph on the right was taken at an exhibition in Furth im Wald
by Detlev Vreisleben on 22 January 2010 .
Whether the device was actually used by the East German
remains to be seen. Unlike other TMS bugs, like the
it does not appear in any Stasi reports that
have been found to date.
It is therefore likely that the Stasi obtained it for evaluation
According to the note in front of the device, it was known in
Czechoslovakia as Štěnice IX, but this is likely to be
incorrect. According to the database of the Czech Police Museum,
Štěnice IX was a combination of devices TRM 500 and 501,
but the device shown in the exhibition is almost certainly a TRM 104.
As the correct Czech name for the device is currently unknown, we
will call it Štěnice 'x' for now.
This is probably also incorrect.
The interior of the TM-104 is fully cast in white artificial rubber, making
it very difficult to inspect its design. It is clear however, that it is
basically a simple free-running FM transmitter, as it exhibits the so-called
hand-effect: the frequency changes when the hand is moved close
This is confirmed by the x-ray 1 above, in which the circuit of a simple
one-transistor transmitter can easily be recognised in the right half. The left
part only contains the microphone and the jack socket for the activation
plug. From this image we also learn that the upper battery contact is the
plus (+) terminal, and that the activation socket simply disconnects the (-)
terminal from the circuit. This means that it can be controlled by
an open-collector output from, say, a switching receiver. It allows the
transmitter to be controlled remotely.
Further x-ray images below.
Images made with Creative Electron TruView Prime.
Document kindly supplied by Detlev Vreisleben .
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© Crypto Museum. Created: Wednesday 12 June 2019. Last changed: Saturday, 15 June 2019 - 20:00 CET.