First Alert BRK CO5120BN Hardwire Carbon Monoxide Alarm with Battery Backup plastic Imported 120-volt hardwired carbon monoxide alarm wires directly into your home's electrical system Electrochemical sensor accurately detects carbon monoxide Microprocessor-controlled to minimize false alarms Easy-to-access battery drawer; 9-volt battery included Can integrate with up to 18 compatible devices for extended coverage Superior carbon monoxide sensor with battery backup Inter-connectable with BRK and First Alert hardwired smoke and carbon monoxide alarms Microprocessor controlled for fewer nuisance alarms Simple to use silence/test button; convenient alarm latch indicator 9-volt battery included; 7-year limited warranty