Designed to meet UL standard 2075 for the Standard For Safety for Gas and Vapor Detector and Sensors * Sensitivity based on UL 1484 Standard for Residential Gas Detectors * Surface mounts to a wall using the supplied enclosure rear housing * Flush mounts in a 2 x 4 (1-1/2 inch deep minimum) single gang switch,or handy electrical box * Small, low profile, attractive unit in a white plastic case