An error detection apparatus for detecting an error in a power signal output by an external device switchable by a switching signal has a comparing unit for comparing the power signal with a reference signal to yield a comparison signal, a switching unit for providing the switching signal dependent on a control signal with the switching unit being designed to disregard the control signal and to ensure that the external device is switched off upon provision of a triggering signal to the switching unit, and a triggering unit for providing the triggering signal depending on the control signal and the comparison signal. Alternatively, the error detection apparatus has an influencing unit for influencing the power signal, such that the power signal fulfils a predetermined relationship to a reference signal in the case of an occurrence of the error, whereas the relationship is not fulfilled in the absence of the error.