Method for measuring distance between two objects and method for controlling access to an object or the use thereof, in particular access control and driving authorization for a motor vehicle

A bidirectional dialogue is carried out between a portable code emitter and a base station for access to a motor vehicle. Both signals are correlated with each other and the dialogue repeated at an altered carrier frequency. The distance of the code emitter from the base station is determined from the difference in two phase difference measurements between the sent and received signal in one station (or ). Access to, or use of the motor vehicle is only permitted when the code emitter is within a certain distance from the motor vehicle.