The invention concerns a device for detecting a faulty positioning between a first element and a second element comprising an electromagnetic wave emitting unit designed to be secured to the first element and an electromagnetic wave receiving and processing unit designed to be secured to the second element. The latter unit co-operates with the electromagnetic wave emitting unit to detect a faulty positioning of the first element relative to the second element. When used for a mobile radiology facility, the first element is, for example, an X-ray generator, and second element is, for example, a radiological image sensor.