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ISMI-Catcher Funkturm von MichaelGaida, lizensiert unter Pixabay License
Freedom in the digital age
Art. 1, 2

IMSI Catcher

Surveillance with IMSI catchers may only be permitted under strict conditions. We submitted an opinion in the Privacy International case in the UK.

The GFF has issued an opinion on the use of IMSI catchers by German police authorities. IMSI catchers are surveillance tools whose use by German authorities is accompanied by notification and reporting obligations. The statement is part of a "Witness Statement" of a case of the partner organization Privacy International in Great Britain, which has been concluded in the meantime. The case concerned the refusal of British police authorities to publicise information about the purchase and use of IMSI catchers. Unfortunately, the lawsuit was unsuccessful.


IMSI catchers are used to monitor people using their cell phones. IMSI stands for International Mobile Subscriber Identity (IMSI). This is a number stored on the mobile phone card that can be used to uniquely identify the card. IMSI catchers pose as the radio cell of a network operator in order to read out the IMSI numbers of cell phones. Due to their stronger signal, cell phones in the immediate vicinity automatically dial into the IMSI catcher. This goes unnoticed by the users.

Once dialed into the ISMI catcher, it can locate the corresponding phone and listen in to calls. In this way, all persons within a certain radius can be monitored and, for example, the participants of demonstrations or other large events can be recorded.


In October 2016, research by the Bristol Cable revealed that various police agencies in the UK had purchased IMSI catchers. Privacy International subsequently submitted a series of Freedom of Information requests to various police agencies, the Home Office, and the National Police Chief's Council. In them, Privacy International requested information about the purchase and use of IMSI catchers by British police.

All authorities contacted stated that they could "neither confirm nor deny" whether they had any relevant information on IMSI catchers. The responsible British data protection authority, the Information Commissioner's Office (ICO), confirmed that the refusal of information on the basis of the "neither confirm nor deny" policy was lawful. Privacy International subsequently filed a complaint against the ICO's decision on August 7, 2018.


The opinion, written by GFF president Ulf Buermeyer, supports these proceedings with an account of the German legal situation. Police authorities in Germany also use IMSI catchers at both the state and federal level. In doing so, they are subject to notification and reporting obligations. If IMSI catchers are used in criminal investigations or in the work of the federal criminal police, the individuals concerned must be informed within 12 months of the end of the measure. In addition, the use of IMSI catchers by federal authorities must be reported to the Parliamentary Control Board, which publishes reports containing key data on the use of IMSI catchers.

In the statement, Ulf Buermeyer also highlights the role of parliamentary inquiries. The use of IMSI catchers became public many times due to parliamentary inquiries on federal and state level. In particular, small inquiries in the state parliaments in Bavaria, North Rhine-Westphalia and Bremen made precise information on the use of ISMI catchers public. The data provide a detailed picture of where and how often IMSI catchers were deployed in each year and state.


The GFF defends fundamental and human rights in Germany - but also beyond. In a country governed by the rule of law, police authorities may not decree the use of surveillance technology as they see fit. Precautions based on the rule of law include not only high preconditions for the use of covert surveillance methods, but also extensive obligations to provide information on the part of the bodies that use them. The "neither confirm nor deny" strategy of the British authorities does not do justice to this, especially since IMSI catchers are a very invasive surveillance technology. With the "Witness Statement", the GFF has shown that the stricter information requirements applicable in Germany are both necessary and practicable. Nonetheless, in December 2019, two UK courts dismissed the case. Privacy International has decided not to appeal.

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