In the German state of Bavaria, dozens of people are in 'preventive detention' because they might otherwise engage in climate protests, specifically around the car industry exposition IAA in Munich.
Apparently possible for a month there...
https://www.zeit.de/gesellschaft/zeitgeschehen/2023-09/letzte-generation-bayern-praeventivhaft-gewahrsam
Actually, Bavaria has a 2 month limit. Schleswig-Holstein is the one with no limit.
Makes sense, they border denmark after all