Abstract: A mounting member for engagement with the housing of a PIR device includes a plurality of elongated, flexible arms for mounting the device in an operative position on a ceiling panel. The arms are hingedly attached to the mounting member and extend to terminal ends which are attached to one another. The arms may be moved toward one another to a flexed position to permit insertion through an opening in the ceiling panel, and return to their unflexed position to engage the panel adjacent the periphery of the opening. A first plurality of relatively short legs having inwardly directed hook portions are provided on the mounting member for engagement with the horizontal flange on an inverted T-shaped track member for supporting ceiling panels. A second plurality of short legs having outwardly directed hooked portions permit engagement of the mounting member with a wall plate having an opening therein.