A method monitors whether the switching threshold of a switching sensor lies within a predefined tolerance region. An input signal is applied to the sensor's signal input, and a signal output emits a switch output signal that takes a first value when the input signal exceeds the switching threshold and, otherwise, takes a second value. A modulator generates a modulator signal used as an input signal that changes continuously or cyclically between an output value defining the upper limit and a smaller test value defining the lower limit of the tolerance region. The switch output signal pulses synchronously with the modulator signal between the first and second values when the switching threshold lies within the tolerance region and otherwise does not pulse. An evaluation device monitors the pulsation, an alarm signal being triggered when the switch output signal does not pulse for at least a predefined test period.