Located on the right and left sides of a housing of an automobile radio for example is one detent spring each projecting from the housing, which spring is retractable to enable insertion of the housing into a mounting slot and which, by rotating a catch, is retractable into the housing. By rotating the catches in the other direction of rotation, the detent springs are again released. Disposed eccentrically on the top side of each catch is a pin for which a guide channel is located in the mounting slot so that the housing may be inserted into the mounting slot only with the detent springs projecting from the housing. After complete insertion of the housing into the mounting slot, the detent springs snap in place against detent edges of the mounting slot to lock the housing in place. To remove the housing from the mounting slot, the detent springs are retracted into the housing by rotating the catch. When the housing is pulled out, the pins abut the mounting slot, thereby rotating the catches into the locked position and allowing the pins to slide through the guide channels. After removal from the mounting slot, the detent springs again snap out of the housing into the locked position. The housing may now be reinserted into the mounting slot and automatically locked after compete insertion since the detent springs engage behind the detent edges without any special procedure being required.