SC9120B Smoke / Carbon Monoxide Combo Alarm 10YR CO Sensor/10YR End of Life. 120V AC/DC Smoke & CO Combo Alarm. 9V Alkaline Battery Backup. Dust Cover. Electrochemical Carbon Monoxide Sensor – the most accuratesensor available as compared to other sensing technologies. End of Life Signal provides audible notification alarmsneeds to be replaced. Hardwired ionization/CO combination alarm meets newconstruction requirements. Latching alarm indicator – remembers which unit initiatedan alarm. Perfect Mount – allows for easy alignment of alarm. Two silence features – can silence the low-batterychirp for up to eight hours or temporarily silence anunwanted nuisance alarm