Universal Security Instruments MCND401B M Series Plug-In Carbon Monoxide and Natural Gas Alarm with 9-Volt Battery Backup offers Single Installation and Double Protection. This compact plug-in alarm is perfect for new or replacement installations. Dual sensing alarm - provides protection against two deadly household threats: Carbon Monoxide and Natural Gas. The display shows the level of carbon monoxide detected. This alarm is suitable for installation in houses, apartments and mobile homes. Early warning of carbon monoxide, natural gas and smoke is best achieved by installing combination alarms on every level of dwelling, including basements. For maximum detection, install an alarm inside every bedroom, outside every sleeping area and on every level of the dwelling. Universal Security Instruments is always working to protect your family. Packaged in a retail box.