First Alert PC900 Battery-Operated Combination Photoelectric Smoke and Carbon Monoxide Alarm N/A Imported Sleek, battery-operated combination smoke and CO alarm Photoelectric sensor detects smoke from smoldering fires while minimizing false alarms Electrochemical CO sensor alerts you to carbon monoxide danger from multiple sources Battery-operated smoke detector requires no rewiring for installation; 9-volt battery included Stylish, low-profile design mounts easily on wall or ceiling