A monitoring unit, for monitoring an elevator system, includes a circuit assembly having a power supply unit for dispensing a grid-dependent first operating voltage and at least one processor-controlled monitoring module to actively and/or passively ascertain state data of the elevator system. An energy storage unit, that dispenses a grid-independent second operating voltage, and a first switching device supply the first operating voltage to the monitoring module during a normal operation and supply the second operating voltage to the monitoring module in the event of a power outage. A non-volatile data storage unit that stores a variable operating parameter and a second switching device deactivate parts of the circuit assembly. The monitoring module actuates the second switching device based on the stored operating parameter that has a first value before the monitoring unit is started and has a second value after the monitoring unit is started.