A detector device for finding concealed studs in partitioning includes a pair of plates which are supplied with ac via resistors. Amplifiers produce outputs representing the sum and difference respectively of the signals imposed on the plates. The sum signal drives a display enabling circuit including a comparator which enables a display means to operate when the sum signal exceeds a threshold level. The difference signal drives two comparators which control three display device such that one display device is operated only when the detector device is over the center of a stud. The other display devices indicate which way the detector should be moved to place it over the center of the stud.