In Germany, using unapproved mobile signal boosters is generally illegal because they can interfere with cellular networks[1][2]. The regulatory authority in Germany is the Federal Network Agency (Bundesnetzagentur)[2]. They require devices to have specific certifications to be approved for use[1][2].
However, the Bundesnetzagentur may allow exceptions for reasons of national security[8]. Despite the regulations, some sources suggest that enforcement is rare, though mobile network operators may locate and insist that unapproved boosters be turned off[1]. Using uncertified signal boosters can lead to fines and equipment confiscation[2].
It's legal to trade repeaters for phone signals in the EU, but they must have specific certifications to be used[1]. Customer satisfaction is a priority for suppliers of approved devices, and these devices are CE-certified and fully compliant with Bundesnetzagentur regulations for use in Germany[3].
Citations:[1] https://www.reddit.com/r/AskAGerman/comments/191j9b2/is_installation_and_using_a_mobile_signal_booster/
[2] https://www.mobilesignalguru.com/blog/legal-requirements-and-regulations-for-mobile-signal-boosters/
[3] https://mysignalboosters.com/de/faqs/
[4] https://www.weboost.com/blog/regulation-myths-about-cell-signal-boosters
[5] https://stackoverflow.com/questions/16993316/boostsignals2-and-exception-handling
[6] https://www.pta.gov.pk/category/unauthorized-non-type-approved-use-import-sale-of-signal-boosters-amplifiers-repeaters-is-prohibited-1359964788-2023-06-01
[7] https://www.bundesregierung.de/breg-en/service/archive/coronavirus-vaccination-faq-1959802
[8] https://jammermaster.com/regulations/the-legal-question-of-signal-jammers-in-germany/