Method of operating a mobile control unit intended to form part of a home-automation installation comprising elements including items of equipment fixed in a building, the elements of the installation communicating over a home-automation network, each element being furnished with an identifier which is specific to it and with an authentication key, termed “common key”, identical for all the elements of the home-automation network and authenticating an element's membership to the home-automation network, characterized in that it comprises:—a step of locating the mobile control unit with respect to a contour containing the elements of the home-automation installation, the mobile unit comprising a means of network linking to the home-automation network,—a step of automatic invalidation of the common key contained in the mobile control unit in the case where the mobile control unit is situated outside the contour.