Abstract: The present invention relates to an apparatus for monitoring an operation of an elevator, the apparatus is configured to: receive a noise signal induced in an analog input of a device associated to an elevator car during an unemployment of the device in its dedicated task; compare the noise signal of the analog input to a reference signal; and set, in accordance with a comparison between the noise signal and the reference signal, a detection result to express one of the following: (i) an operation of the elevator is proper, (ii) the operation of the elevator is improper. The invention also relates to a method, to a computer program product, and to an elevator system.