Mit einer Funkanlage dürfen nur solche Nachrichten abgehört oder in vergleichbarer Weise zur Kenntnis genommen werden, die für den Betreiber der Funkanlage, für Funkamateure im Sinne des § 2 Nummer 1 des Amateurfunkgesetzes, für die Allgemeinheit oder für einen unbestimmten Personenkreis bestimmt sind.
Which in English would read something like this:
With radio equipment you are only allowed to listen to, or take note of in some other way, those messages that are addressed to the operator of the equipment, those messages that are addressed to ham radio operators in general, those messages that are addressed to the general public or for an undefined group of people.
This is of course absolutely unenforceable, untraceable and generally ridicoulus, but it is what it is. Imagine your neighbours having very loud arguments (or very loud 'horizontal discussions') in a clairaudient flat, and then telling you that you cannot listen to it. And being correct legally ;)