The invention relates to a method for operating a locking system for a motor vehicle, wherein the locking system has a motor-vehicle-based controller and a portable ID transmitter (1) that has at least a first operating mode and a second operating mode, of which the second operating mode is designed as an energy-saving mode. The ID transmitter (1) has a power supply battery (2), a motion sensor (3), a microcontroller (4), a transmission and reception circuit (5) and an LF reception circuit (6). A set of state values that is dependent on a usage mode of the motor vehicle is transmitted to the ID transmitter (1) by means of the motor-vehicle-based controller. The activation of the energy-saving mode is performed on the basis of the set of state values. The invention moreover relates to a portable ID transmitter (1) and a locking system.