The BRK 1046431 (model CO250B) is the special contractor pack offering of our basic 9V battery-operated carbon monoxide alarm. This alarm is perfect for use in existing multi-family facilities such as apartment, dormitory or hotel applications. Battery installation and removal can occur while the unit is mounted to the ceiling or wall via the hinged cover. To insure the battery is always replaced properly, the cover is designed to resist closing when the battery is missing. Designed for wall or ceiling mounting. Includes mounting anchors and screws. Ships as a 4-pack. 10-Year Limited Warranty.