Switch for controlling an electrical appliance, comprising: a switch housing; a display; an actuation element projecting from the switch housing, which can activate at least one contact of the appliance when it is moved from an OFF position to an ON position, wherein changing the switching state changes an operating state of the electrical appliance and/or the display; a microprocessor disposed in the switch housing, by means of which the operating state of the appliance and/or the display can be changed by comparing a determined actual value with a stored maximum value for a system state; means for selecting a maximum value from a set of selectable maximum values for a desired system state stored in the microprocessor, characterized in that one initial value and one maximum value each are stored in the microprocessor for all system states available for selection; such that, when the electrical appliance is initially activated by the actuation element, the microprocessor initiates an identifier for different signals determined by the microprocessor which is displayed through the display, wherein the different signals correspond to different system states; and such that selection of one said different system state for the electrical appliance can be effected by actuating the actuation element, whilst a corresponding said signal associated with this system state is active at the display, wherein the associated maximum value for operating the electrical appliance also being set by the said actuation of the actuation element; wherein reaching or exceeding the maximum value for the selected system state can be indicated by a warning signal produced by the microprocessor. a switch housing; a display; an actuation element projecting from the switch housing, which can activate at least one contact of the appliance when it is moved from an OFF position to an ON position, wherein changing the switching state changes an operating state of the electrical appliance and/or the display; a microprocessor disposed in the switch housing, by means of which the operating state of the appliance and/or the display can be changed by comparing a determined actual value with a stored maximum value for a system state; means for selecting a maximum value from a set of selectable maximum values for a desired system state stored in the microprocessor, characterized in that one initial value and one maximum value each are stored in the microprocessor for all system states available for selection; such that, when the electrical appliance is initially activated by the actuation element, the microprocessor initiates an identifier for different signals determined by the microprocessor which is displayed through the display, wherein the different signals correspond to different system states; and such that selection of one said different system state for the electrical appliance can be effected by actuating the actuation element, whilst a corresponding said signal associated with this system state is active at the display, wherein the associated maximum value for operating the electrical appliance also being set by the said actuation of the actuation element; wherein reaching or exceeding the maximum value for the selected system state can be indicated by a warning signal produced by the microprocessor.