Abstract: An apparatus that attaches itself to a surface by negative pressure and that can move over the surface, in particular, for carrying out work, to prevent a risk, depending on the alignment of the surface, of the apparatus dropping downward if there is a decrease in an attachment force in the case of malfunctioning includes a safety configuration that monitors detachment of the apparatus from the surface and, in such a case, attaches a retaining configuration, preferably in the form of a suction cup, to the surface, the retaining configuration retaining the movable apparatus on the surface.