Abstract: An apparatus for alternately retaining a selected one of a pair of keys and releasing the other one of the pair of keys is provided. The retained key cannot be released until the other key is again disposed in a retained position. The apparatus includes a base plate having a pair of key receptacles, a slider member slidably mounted on the base plate, a visitor key having a pinion gear and a home key. The slider member includes a pair of key retaining slots for respectively retaining each key and a rack for driving engagement by the visitor key pinion gear for effecting sliding movement of the slider member in response to rotation of the visitor key pinion gear. A conventional key can be secured to the home key to control use of the conventional key through the selected release and retention of the visitor key and the home key.