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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 COT 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 COT did not go unnoticed. Intelligence service BVD (now: AIVD) mentioned the group in its monthly bulletin [1] of November 1990, and called it a structural security problem. According to the BVD, two COT members had recently appeared in a national television show, in which they disclosed secret police locations.
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, COT 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 two COT members in a rented car, observing the Dutch police during the high-profile kidnapping case of Dutch Ahold top manager Gerrit-Jan Heijn, in 1987 and 1988. Although the police had encrypted its carphone communications — using Telsec 02 devicesCOT was still able to determine their location.

COT 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 homemade ATF-1 sets used by the COT, placed on the co-seat of a regular car. 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].

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 as Service Department of the Underworld.
ISM Tracker

In the 1980's and 90's, COT equipment turned up in several criminal investigations and in a number of court cases. Most of the devices were developed by hobbyists, hackers and technical students. Most of them were initially unwitting of the fact that the equipment was used for criminal activities and when they eventually found out, they generally left the hackers-scene.

COT equipment on this website
Home-made ATF-1 carphone phreaking unit
ISM-band telemetry transmitter used as vehicle tracker
Telephone line bug (POTS)
Homemade RF transmitter hidden in a telephone microphone element
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. Euro Foto, Image of COT members observing the police in 1987-1988
    Unknown author and date. Obtained January 2020.

  3. Anonymous former COT member, Photographs of COT operation and equipment
    Obtained December 2019.
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Crypto Museum. Created: Tuesday 04 February 2020. Last changed: Tuesday, 05 January 2021 - 09:44 CET.
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