The invention relates to a method for detecting parked vehicles and for collecting parking fees, wherein a transponder arranged in a vehicle repeatedly emits a detection signal which is received by at least three radio devices. On the basis of the detection signal, a position of the vehicle is calculated and an identifier of the transponder is determined, wherein it is detected whether the vehicle is in a parking space area and is parked. If the vehicle uses a parking space area for parking, an identifier of the transponder is transmitted to a registration server which determines a parking fee on the basis of a tariff for the parking space area which is used and, if necessary, initiates a payment process.