A method for protecting a nonmobile work machine driven by an electric motor, at least one measured value of a time-critical parameter of the work machine being determined via a measuring unit, the work machine being switched off when the determined measured value of the time-critical parameter is outside a predefined setpoint range, and the determined measured value of the time-critical parameter being quantized in a level signal (i1, i2, i3, i4) and transmitted as a first signal to an evaluation unit via an interface, characterized in that a second signal for further information concerning the work machine, to be transmitted from the measuring unit to the evaluation unit, is modulated to the first signal.