A sensor unit (10, 110) configured to detect operation events of an automatic dispenser, the operation events comprising dispensing events, the sensor unit (10, 110) comprising: a detection unit configured to detect a sequence of changes (36A-D) in an operating voltage of the dispenser; and a controller configured to: - analyse the voltage changes (36A-D) for predetermined characteristics to detect a voltage change that is related to a dispensing event of the dispenser; - assign one of the detected voltage changes (36B, 36C, 36D) to a dispensing event of the dispenser based on the analysis, wherein a second voltage change preceding a third voltage change that is related to the dispensing event is indicative of a start of an electric motor of the dispenser and is assigned to a start of the dispensing event based on a voltage decrease having an amplitude falling below a first detection threshold over a certain period of time as a predetermined characteristic, wherein the third voltage change related to the dispensing event lasts a longer time span and requires a fewer amount of energy than the preceding second voltage change and is assigned to the dispensing event during which the electric motor repeatedly moves a mechanical member of the dispenser based on a continuous increase of the voltage as a predetermined characteristic, and wherein the time span of the third voltage change related to the dispensing event ends with detection of a following fourth voltage change during which the electric motor consumes fewer energy over a shorter period of time than during the third voltage change related to the dispensing event, wherein the following fourth voltage change is assigned to a recovery process of the dispenser based on an amplitude of the voltage increase as a predetermined characteristic; and - create a dataset indicative of the dispensing event and the time span of the third voltage change related to the dispensing event. a detection unit configured to detect a sequence of changes (36A-D) in an operating voltage of the dispenser; and a controller configured to: - analyse the voltage changes (36A-D) for predetermined characteristics to detect a voltage change that is related to a dispensing event of the dispenser; - assign one of the detected voltage changes (36B, 36C, 36D) to a dispensing event of the dispenser based on the analysis, - analyse the voltage changes (36A-D) for predetermined characteristics to detect a voltage change that is related to a dispensing event of the dispenser; - assign one of the detected voltage changes (36B, 36C, 36D) to a dispensing event of the dispenser based on the analysis, wherein a second voltage change preceding a third voltage change that is related to the dispensing event is indicative of a start of an electric motor of the dispenser and is assigned to a start of the dispensing event based on a voltage decrease having an amplitude falling below a first detection threshold over a certain period of time as a predetermined characteristic, wherein the third voltage change related to the dispensing event lasts a longer time span and requires a fewer amount of energy than the preceding second voltage change and is assigned to the dispensing event during which the electric motor repeatedly moves a mechanical member of the dispenser based on a continuous increase of the voltage as a predetermined characteristic, and wherein the time span of the third voltage change related to the dispensing event ends with detection of a following fourth voltage change during which the electric motor consumes fewer energy over a shorter period of time than during the third voltage change related to the dispensing event, wherein the following fourth voltage change is assigned to a recovery process of the dispenser based on an amplitude of the voltage increase as a predetermined characteristic; and - create a dataset indicative of the dispensing event and the time span of the third voltage change related to the dispensing event. - create a dataset indicative of the dispensing event and the time span of the third voltage change related to the dispensing event.