Abstract: A sensor apparatus for the non-contact monitoring of a predetermined end position of a mechanical element, in particular a door in an aircraft, is provided which comprises a probe, an electronic measurement means, and a control means. The probe is attached to the aircraft and samples the distance between itself and a target surface on the element to be monitored. The electronic measurement means is connected to the probe and is so constructed that in response to at least one control signal it generates a measurement signal corresponding to the distance. The control means is connected to the electronic measurement means and generates the control signals, receives measurement signals and generates an indicator signal to indicate that the end position has been detected.