The First Alert SC9120B Hardwired Combination Ionization Smoke and Carbon Monoxide Alarm with Battery Backup delivers both smoke and carbon monoxide detection in a single unit. This 120-volt AC smoke detector uses an ionization smoke sensor to reliably detect smoke from hot, fast-flaming fires. It also features an advanced electrochemical sensor that detects carbon monoxide leaks from multiple sources such as faulty fuel-burning appliances and blocked chimneys. If a threat is detected, the alarm sounds a loud siren that helps alert you to danger. Designed to be hardwired directly into the electrical system of your home or facility, this 120-volt hardwired smoke detector features a backup battery that helps keep the alarm functioning even in the event of a power outage. A universal mounting bracket makes installation easy and helps hide drywall cutouts, while tamper-resistant locking pins keep the alarm secure. And thanks to the convenient test/silence button, you can easily check whether the alarm is functioning properly and mute false alarms. This smoke and carbon monoxide alarm can integrate with up to 12 other First Alert or BRK hardwired alarms and features a latching indicator that identifies which unit triggered the alarm. Ideal for coverage of larger areas, this pack of 12 alarms can help you protect your entire home or facility from carbon monoxide leaks and fires.