Abstract: A user identification device for an access system and/or starting system of a vehicle has an energy source such as a battery or an accumulator for making available a supply voltage. In addition, there are provided a measuring device for sensing the supply voltage currently made available by the energy source and an open-loop control and evaluation device for comparing the sensed current supply voltage with a first predetermined threshold value voltage and for detecting at least one function of a plurality of functions which can be carried out by the open-loop control and evaluation device when the current sensed supply voltage drops below the first predetermined threshold value voltage. By deactivating specific functions when the energy source becomes weak while other specific functions remain activated, the critical state of the energy source of the user identification device can be signaled to a user without additional display devices being necessary.

Abstract: Through a microcontroller, control signals are transferred to a transmitting and receiving unit or configuration data are transferred. Through the transmitting and receiving unit, in a first operating state transmission signals are issued, while controlling the control signals of the microcontroller. Upon a first specified event, the transmitting and receiving unit is switched to a second operating state through a one-time transfer of corresponding configuration data by the microcontroller. In the second operating state, the transmitting and receiving unit automatically transmits repeated transmission signals. The microcontroller immediately switches to a current-saving or non-current, inactive operating state after said microcontroller has switched the transmitting and receiving unit to the second operating state.