Abstract: The present invention relates to a device for locating in buildings the exact position of hidden objects, preferably boxes for electrical installations which are to be exposed by providing a hole in a covering building unit, such as a platelike wall, roof, or floor unit, substantially opposite the object. The locating device may be used for all known types of covering building units without complicating rational mounting of the covering building unit. The locating device according to the invention comprises a locating magnet having a first magnetic body which is mounted on the object at one side of the building unit hiding the object, and a second magnetic body which is movable along the other side of the building unit for sensing the position of the first magnetic body mounted at the object.