A system for mounting and retaining an electronic device in an opening in a door or panel comprises a power monitoring device for monitoring characteristics of the power transmitted through one or more power lines. An apparatus is coupled to the power monitoring device and is adapted to secure the power monitoring device within the panel opening by engaging at least one surface of the panel. The power monitoring device may include a meter base and a display module. The combined meter base/display module assembly or remote-mounted display module may be mounted and retained in the door or panel opening.