Yes, GPS trackers can be taken onto an airplane in your suitcase.
This was also confirmed to us in writing by the airline Eurowings:
We allow a GPS tracker that is switched on and packed in a suitcase. In principle, there are no objections to taking this item with you in your checked baggage.
From a legal point of view, it would only be problematic if you took the GPS tracker with you in your hand luggage and refused to switch it off when asked to do so.
However, if you put the tracker in your suitcase and it becomes apparent during the loading process that it is emitting interfering signals, in the worst case scenario the suitcase would have to be stored at the airport. Passengers will then be contacted to discuss how to proceed. However, it is not illegal to carry a GPS tracker that is switched on.