Safety devices are subject to the building regulations and are only permitted if they bear the mark of conformity (Ü mark) from the German Institute for Building Regulations (DIBt)!
Source: State Building Code § 20 Building Products (1)

When buying, pay attention to the DIBt approval!

Your exhaust air control (window contact switch) should definitely have a DIBt approval so that you can be sure to get the highest possible safety. Your chimney sweep will also look for this test when recommending such a system.