The invention relates to a method for verifying a prescribed maximum physical distance (MAX) of a radio key (11) in relation to a motor vehicle (10), wherein a control apparatus (26) uses a radio device (21) of the motor vehicle (10) to transmit at least one electromagnetic radio signal to the radio key (11) and subsequently receives a respective electromagnetic response signal and, for each radio signal, takes the radio signal and the associated response signal as a basis in each case for using a signal propagation delay measurement to ascertain a respective signal propagation delay and checks whether the signal propagation delay fails to satisfy a predetermined propagation delay criterion (27), and signals a transgression above the propagation delay (28) when the propagation delay criterion (27) is not satisfied.