Covert surveillance detection receiver
- wanted item
SRR-100 was a covert body-worn receiver,
or scanner, developed in the 1970s by the
Office of Strategic Services (OTS)
and the Office of Communications (OC) of the US
Central Intelligence Agency (CIA),
and probably 1 manufactured by Motorola.
It was used during the Cold War
the radio communications
of Soviet and other Eastern Bloc surveillance teams, and
comprises a miniature receiver, an inductive neckloop/antenna
and a wireless Phonak earpiece.
The basic version measures 96 x 54 x 12 mm.
It has two knobs at the top, one for controlling the volume and one
for selecting the desired mode of operation.
At the left is a 4-pin socket for the neckloop.
At the bottom is a
circular screw that gives access to the battery compartment.
The unit is powered by two 1.35V mercury batteries.
The neckloop serves two purposes: it is used as the antenna, and as an
inductive loop or coil for delivering audio to the
wireless Phonak earpiece.
The receiver is capable of intercepting FM radio signals in the 102 MHz
band (4 metres), that use
inversion-based speech scrambling.
It was usually carried in a cloth harness or pocket under
the clothing of the CIA operative. It was deployed in Eastern Block
countries like Russia (USSR) and East-Germany (DDR), to ensure that the
operative was black, which means that he or she was free from
The image on the right shows a close-up of the SRR-100 as described in
surviving MfS (Stasi) 2 reports about
confiscated US covert equipment.
The SRR-100 is similar to the Russian Kopchick receiver,
which serves the same purpose. It was developed around the same time as
the SRR-100, but it is currently unknown who was first. The SRR-100 seems
to be the more advanced one, as it uses a wireless Phonak earpiece.
Unlike the SRR-100 however, the Kopchik was a non-selective or
aperiodic receiver, which means that it could pickup any signal in
its vicinity, regardless the frequency.
This is unconfirmed, but seems likely when considering the construction
and the selected materials, such as the knobs. At the time, Motorola had a
Goverment Electronics Division,
that worked exclusively for
US intelligence agencies
like the CIA and the NSA.
Ministerium für Staatssicherheit (MfS), commonly abbreviated as
Stasi, was the repressive intelligence and secret police organisation
of the former DDR (East-Germany).
Help required —
We are looking for detailed information about the SRR-100 receiver and,
if possible, a working unit. If you can provide any of these, or any
other information, please contact us
The diagram below shows the various features of the SRR-100 when looking
at the device from the front. The controls and connections are in a
recessed area at the top. The two knobs at the centre are for volume
control and mode of operation selection. At the left is a 4-pin
socket for connection of the induction loop, which also acts as the
antenna. The induction loop is carried around the neck and passes
the audio to the Phonak earpiece. The loop also acts as the antenna.
At the right is the recessed TEST push-button, which should be pressed
to check the operation of the device. The unit is powered by two 1.35V
mercury batteries (connected in parallel) that are installed via the
hinged access door at the bottom. Depending on the
setting of the audio volume, the batteries allow between 3 and 10 hours
of uninterrupted operation. According to the handwritten marking on
the front panel, the device was last check and approved on 19 July 1979.
The MODE-selector on top of the device has the following settings:
SStandby (AFC disabled)
There were at least two versions of the SRR-100:
the initial single-channel version, and an expanded version with
six channels. The diagram below shows the top panel of the single-channel
version, which is just 12 mm thick. Crystal and batteries are installed
at the bottom.
This version is suitable for the entire 101.8 - 103.4 MHz
frequency range, but can only receive one channel at a time. This
means that the frequency used by the Russian surveillance teams had
to be determined carefully before each mission, after which a
suitable crystal was installed in the SRR-100.
The device found by the KGB on CIA officer
Martha Peterson when
she was arrested in Moscow on 15 July 1977, was of this type.
It was fitted with a crystal for 103.25 MHz  .
The enhanced version is suitable for six crystal-based channels in
the 102 MHz range. It is shown in the photograph below and is
basically a standard SRR-100 with an additional module bolted
to its rear side. The colour of the add-on
is different (darker) than the basic unit, which suggests that
it was added later, perhaps as an aftermarket upgrade. The combined
top panel is shown below.
At the left is a coaxial socket that might have been used for the
connection of an antenna. At the right is a white push button that is
used for the selection of one of the six channels.
The rear unit is bolted to the basic unit. This was probably done by
removing the rear panel from the SRR-100 and fitting the expansion
unit in its place. The add-on holds the crystals for the
6 channels, which are accessible from the bottom. The interior is
shown further down this page.
The photographs above was found in a report of the Russian intelligence
service KGB, probably from the early 1980s, and was taken after a CIA
officer had been caught with an SRR-100 and several other items.
It shows the Mark II version of the SRR-100. To its right
are two canisters with spare mercury batteries. At the front left
is the inductive loop and the Phonak earpiece.
The image below shows a complete SRR-100 kit, consisting of the SRR-100
receiver unit (left), a neckloop that acts at the antenna and as inductive
audio coil, a white cloth holster or body harness, a phonak earpiece
and a set of spare hearing aid button-type batteries for the earpiece.
The photograph is taken from Stasi reports about confiscated equipment .
Click to enlarge.
The device in the image is the original SRR-100 (i.e. Mark I),
that did not have the bolted-on modification. The body harness was
designed for the male body, and was less suitable for females,
which is why CIA officer
made her own cloth pocket.
The SRR-100 set consists of the following parts:
- SRR-100 receiver
- Phonak earpiece
The wireless earpiece is made by Phonak in Switzerland,
and consists of a pick-up induction coil, a battery, an amplifier
and a miniature loudspeaker. It operation is similar to a
hearing aid which is set to telephone-input.
To make the earpiece invisible, the CIA made silicone reproductions
of the operative's real ears, that obscured the Phonak device.
The image below shows the kind of equipment the the Russian KGB
(now: FSB) found on American agents during the Cold War .
At the rear left, just in front of the leftmost portable radio, is
an SRR-100 receiver with inductive neckloop.
The SRR-100 was probably recovered from CIA case officer
Martha Peterson when she was arrested
on 15 July 1977 after making a dead drop for the Russian spy
Aleksandr Dmitrievich Ogorodnik, codenamed TRIGON.
Click for a close-up
The online magazine WIRED has made an interesting series
of YouTube videos, in which Jonna Mendez — former CIA Chief of Disguise
of the Office of Technical Service (OTS) of the CIA — talks about some of the
tactics and gadgets they used during the
In the episode below she explains how the SRR-100 receiver was used
during surveillance detection runs in Moscow .
Former CIA Chief of Disguise Jonna Mendez explains how
the SRR-100 was used 
Below is the only photograph of the interior of an SRR-100, that was found
in a KGB/Stasi report of the 1980s. It shows the interior of the add-on
of an SRR-100 Mark II (i.e. the part that is bolted to the rear
of the basic unit). At the top is the white push button for selection of
the desired channel. At the bottom are the crystals for the six channels
in the 102 MHz range.
At the center is a double-sided printed circuit board (PCB) that is populated
with miniature components. Judging from the layout and the lack of a solder-mask,
it was part of a small hand-assembled series. At the left are three (white)
integrated circuits (ICs) that were probably made by RCA.
At the bottom right is a coaxial cable that connects the expansion unit
to the basic receiver.
In the 1970s, the Soviet Union (USSR) introduced its own surveillance detection
receiver, which was also body-worn and was able to detect a wide range of
nearby radio signals, in particular those in the 150 and 400 MHz bands.
The image on the right shows the Russian device, which was known as Kopchik
➤ More information
Mark IIColour photograph of a device dated 19 July 1979 
Mark IStasi report about KGB-confiscated SRR-100 
DesignOC, OTS 
BandVHF-M, (4 metre band)
Frequency101.8 - 103.4 MHz
Sensitivity0.16µV @ 10dB S/N, 0.3µV @ 20dB S/N
AFCat 0.2µV input
Deviation7 - 10 kHz
IF17.9 MHz (with crystal filter)
Response420 - 1250 Hz ±3dB
Output100 mW into inductive loop
EarphonePhonak wireless inductive earpiece
AntennaShared with inductive loop
SecuritySpeech scrambling (inversion) around 3050 Hz ±20Hz
Range500 mA (against 100 mW transmitter)
Battery2 x RM-625 mercury cell @ 1.35V (connected in parallel)
Current2.5 - 60 mA (depending on AF volume)
Life3 - 10 hours
Dimensions96 x 54 x 12 mm
Unconfirmed, but very likely.
PurposeWireless earpiece (hearing aid)
DimensionsØ 12.5 x 18 mm
- 102.95 MHz
- 103.00 MHz
- 103.05 MHz
- 103.15 MHz
- 103.25 MHz
- 103.35 MHz
- Unknown author, Photograph of CIA equipment found in Moscow
Date unknown. 1
- MfS, Photographs of SRR-100 device
MfS - HA II, Nr. 42925, BStU 0242-0243. 1
- Wired: Former CIA Chief of Disguise Breaks Down Cold War Spy Gadgets
25 November 2020.
- Antonio & Jonna Mendez, The Moscow Rules
ISBN 978-154173009-0 (2019) / ISBN 978-154176219-0 (2021).
- Detlev Vreisleben, personal correspondence
- Louis Meulstee, SRR-100
Wireless for the Warrior - Volume 4, Supplement chapter 220.
Version 1.00, October 2019.
- Bundesbeauftragte für die Stasi-Unterlagen (BStU) 1
Federal Commissioner for the Stasi-Records.
- MfS, Mitteilung 726/78 (in German language) 3
Abteilung 26. Nr. 1939. 8 June 1978. 4 pages.
Document kindly supplied by Jörg Drobick.
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.
Document obtained from BStU  and kindly supplied
by Detlev Vreisleben .
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© Crypto Museum. Created: Wednesday 18 January 2017. Last changed: Wednesday, 26 May 2021 - 13:37 CET.