Device and method for monitoring a maintenance mode of an elevator installation

A control unit, an elevator-monitoring apparatus and a method are used to monitor a maintenance mode of an elevator installation. The control unit has a controller and a memory device, wherein the controller receives a first signal when a locking device of shaft door is locked and receives a second signal when the locking device is unlocked. The controller compares a chronological signal sequence of first signals and second signals with a reference sequence stored in the memory device for actuation of the locking device and, if the signal sequence of the first signals and second signals matches the reference sequence, ends the maintenance mode and releases a car of the elevator installation for a traveling operation.