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Counter Observation Team

In the Netherlands, in the 1980s and 1990s, the so-called Counter Observation Team — Dutch: Contra Observatie Team — commonly abbreviated to COT, was a highly skilled group of hobbyist scanner-listeners, who observed the methods and covert operations of the Dutch police and the Dutch intelligence services, by intercepting their radio traffic and by using radio direction finding.

Contrary to regular scanner listeners – which were 'just' annoying – the members of the
were described by the police and the intelligence services as damaging, as they directly interfered with – and often frustrated – existing operations.

The existence of the
did not go unnoticed. Intelligence service BVD (now: AIVD) mentioned the group in its monthly bulletin of November 1990, and called it a structural security problem [1]. According to the report, members Henny Kasteleijns and photographer Cocky Toorenspits had recently appeared on national television [1].
Freelance press photographer Henny and his partner, observing the police during the Gerrit-Jan Heijn case (1987-1988). Copyright Euro Foto [3], reproduced here by kind permission [4].

For their work,
used a variety of high-tech equipment, consisting of (modified) commercial-of-the-shelf products, as well has home-made devices. It allowed them to intercept police (radio) communication and determine the position of members of official observation teams, using RDF.

The image above shows
member Henny Kasteleijns and a partner, observing the Dutch police during the kidnapping case of Dutch Ahold Manager Gerrit-Jan Heijn, in 1987 and 1988. Although the police had encrypted its carphone communications – using a Telsec 02
was still able to determine their location.

also made clandestine use of the national ATF-1 carphone network, by using commercial radio equipment, and combining it with a home-made device that emulated the digital handshake signals, allowing them to make free phone calls.
Equipment for clandestine use of the Dutch ATF-1 carphone network [3].

The image above shows one of the clandestine ATF-1 sets used by the
, placed on the co-seat of one of their vehicles. Central to the set was a square aluminium unit that imitated the telemetry signals of a regular (legal) carphone, also known as an ATF-1 phone phreaking unit.

The group had also bugged some of the the vehicles of the Dutch police and the BVD with (radio) trackers, so that their presence could be detected during an operation. Needless to say that this capability soon attracted the attention of criminals, who were willing to pay good money to get access to such facilities [1][2].

This is one of the reasons that the group behind the COT developments, was known by the law enforcement community as Criminal Facilities Bureau (Dutch: Crimineel Facilitair Bureau) and also Service Department of the Underworld [5].
ISM Tracker

COT equipment turned up in criminal investigations and in several court cases [5]. Much of it was developed by hobbyists, hackers and technical students, most of which were initially unwitting of the intended criminal use of the products. When they found out, they generally left the hackers-scene. One former developer claims that his past participation has hindered him later in life [6].

COT equipment on this website
Home-made ATF-1 carphone phreaking unit ISM-band telemetry transmitter used as vehicle tracker Telephone line bug (POTS) Crystal-controlled transmitter (bug) with Motorola pager as switch receiver Pocket organiser with built-in fax machine (1994) used for covert communication
More equipment will be added in due course.

  1. BVD Maandbericht November 1990, Scannerfreaks
    Binnenlandse Veiligheidsdienst (now: AIVD). 2135137-65. (Dutch)

  2. Mark van Dongen en René Zwaap, De Bende van barry
    De Groene Amsterdammer, nr. 35, 27 August 1997. (Dutch)

  3. Euro Foto, Image of COT members observing the police in 1987-1988
    Unknown author and date. Obtained January 2020.

  4. Anonymous former COT member, Photographs of COT operation and equipment
    Obtained December 2019.

  5. Anonymous former law-enforcement officer, Interview and personal correspondence
    February 2020.

  6. Former COT developer 'The Key', Interview and personal corresponcence
    April 2018.

  7. Harry Lensink en Maurits Martijn, De geheimen van een supertapper
    Vrij Nederland, 12 August 2011. (Dutch)
Further information
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Crypto Museum. Created: Tuesday 04 February 2020. Last changed: Saturday, 08 February 2020 - 16:27 CET.
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