Abstract: A flush mounted assembly for housing an electronic or electro-mechanical module which detects abnormal conditions and responds to the detection of such abnormal conditions. The assembly includes a base mounted in an opening in a structural member such as a wall, partition or ceiling. The base includes a peripheral wall defining a shallow cavity with an outer open face and an inner wall. A laterally outwardly projecting flange extends from the peripheral side wall of the base for flush engagement with the structural member. The shallow cavity of the base is dimensioned to receive the electronic or electro-mechanical module. A closure plate is provided for the open outer face of the base. The closure face has a periphery dimensioned to close the open outer face of the shallow cavity in the base leaving only a narrow gap between the closure plate periphery and the base periphery wall to allow ambient air to enter the shallow cavity of the base and interact with the module.