Detection apparatus for detecting the switching state of an electromagnetic switching device, the detection apparatus having the following features: - It has a housing in which a plunger is movably mounted. - The plunger can be moved between two mechanical end positions, the end positions of the plunger corresponding to the switching state of the electromagnetic switching device. - A sensor apparatus is disposed in the housing, said sensor apparatus being able to detect in which of the end positions the plunger is located and to emit an electrical signal corresponding thereto. - The sensor apparatus is embodied such that it is able to detect the position of the plunger without touching the plunger, characterised in that a conditioning circuit is disposed in the housing and conditions the electrical signal, which was emitted by the sensor apparatus, into a message and outputs the message via a communication interface, wherein the housing and the plunger are coordinated in such a way that it can be identified visually from outside the housing in which of the end positions the plunger is located and wherein the housing of the detection apparatus is a different housing from the housing of the electromagnetic switching device and the plunger of the detection apparatus is a different plunger from the plunger of the electromagnetic switching device, that the housing of the detection apparatus can be fixed to the housing of the electromagnetic switching device, and that the plunger of the detection apparatus can be connected to the plunger of the electromagnetic switching device, such that the plunger of the detection apparatus moves together with the plunger of the electromagnetic switching device. - It has a housing in which a plunger is movably mounted. - The plunger can be moved between two mechanical end positions, the end positions of the plunger corresponding to the switching state of the electromagnetic switching device. - A sensor apparatus is disposed in the housing, said sensor apparatus being able to detect in which of the end positions the plunger is located and to emit an electrical signal corresponding thereto. - The sensor apparatus is embodied such that it is able to detect the position of the plunger without touching the plunger, characterised in that a conditioning circuit is disposed in the housing and conditions the electrical signal, which was emitted by the sensor apparatus, into a message and outputs the message via a communication interface, wherein the housing and the plunger are coordinated in such a way that it can be identified visually from outside the housing in which of the end positions the plunger is located and wherein the housing of the detection apparatus is a different housing from the housing of the electromagnetic switching device and the plunger of the detection apparatus is a different plunger from the plunger of the electromagnetic switching device, that the housing of the detection apparatus can be fixed to the housing of the electromagnetic switching device, and that the plunger of the detection apparatus can be connected to the plunger of the electromagnetic switching device, such that the plunger of the detection apparatus moves together with the plunger of the electromagnetic switching device.