Access system for a vehicle, having the following features: a vehicle transmitting/receiving device for emitting one or more query signals (AS1, AS2); at least one mobile identification transmitter (IDI, IDA) comprising: - an identification transmitter control device for outputting control signals and - an identification transmitter transmitting/receiving device - for receiving query signals (AS1, AS2) from the vehicle transmitting/receiving device and - for evaluating signal properties of the one or more query signals at at least two different times, characterized in that the identification transmitter control device is set up - to output a deactivation signal for deactivating the at least one mobile identification transmitter, in particular the identification transmitter transmitting/receiving device, in the event of a change (ΔFS, ΔFR) with respect to the signal properties evaluated at at least two different times which is less than or equal to a predetermined threshold value (SFS, SFR) and - to output a locking signal for locking at least one door of the vehicle in the event of a change (ΔFS, ΔFR) with respect to the signal properties evaluated at at least two different times which is greater than the predetermined threshold value. a vehicle transmitting/receiving device for emitting one or more query signals (AS1, AS2); at least one mobile identification transmitter (IDI, IDA) comprising: - an identification transmitter control device for outputting control signals and - an identification transmitter transmitting/receiving device - for receiving query signals (AS1, AS2) from the vehicle transmitting/receiving device and - for evaluating signal properties of the one or more query signals at at least two different times, characterized in that the identification transmitter control device is set up - to output a deactivation signal for deactivating the at least one mobile identification transmitter, in particular the identification transmitter transmitting/receiving device, in the event of a change (ΔFS, ΔFR) with respect to the signal properties evaluated at at least two different times which is less than or equal to a predetermined threshold value (SFS, SFR) and - to output a locking signal for locking at least one door of the vehicle in the event of a change (ΔFS, ΔFR) with respect to the signal properties evaluated at at least two different times which is greater than the predetermined threshold value. - an identification transmitter control device for outputting control signals and - an identification transmitter transmitting/receiving device - for receiving query signals (AS1, AS2) from the vehicle transmitting/receiving device and - for evaluating signal properties of the one or more query signals at at least two different times, characterized in that the identification transmitter control device is set up - to output a deactivation signal for deactivating the at least one mobile identification transmitter, in particular the identification transmitter transmitting/receiving device, in the event of a change (ΔFS, ΔFR) with respect to the signal properties evaluated at at least two different times which is less than or equal to a predetermined threshold value (SFS, SFR) and - to output a locking signal for locking at least one door of the vehicle in the event of a change (ΔFS, ΔFR) with respect to the signal properties evaluated at at least two different times which is greater than the predetermined threshold value. - for receiving query signals (AS1, AS2) from the vehicle transmitting/receiving device and - for evaluating signal properties of the one or more query signals at at least two different times, - to output a deactivation signal for deactivating the at least one mobile identification transmitter, in particular the identification transmitter transmitting/receiving device, in the event of a change (ΔFS, ΔFR) with respect to the signal properties evaluated at at least two different times which is less than or equal to a predetermined threshold value (SFS, SFR) and - to output a locking signal for locking at least one door of the vehicle in the event of a change (ΔFS, ΔFR) with respect to the signal properties evaluated at at least two different times which is greater than the predetermined threshold value.