Universal Security Instruments M Series Plug-In Carbon Monoxide and Natural Gas Alarm with 9 -Volt Battery Backup, Model MCND401B Reliable plug-in carbon monoxide and natural gas alarm Microprocessor intelligence helps eliminate nuisance alarms caused by non-hazardous sources Compact design covers only one outlet  No wiring required Designed with end-of-service life warning signals and a digital display screen to provide CO parts per million levels and displays "GAS" Comes with a limited warranty