BRK First Alert - SC9120B Hardwired Combination Smoke/ CO Alarm 4K It's a recessed box so

It's a recessed box so plugs don't extend past the wall like they do in a regular box

With advanced photoelectric and electrochemical sensors

Its enhanced sensing technology minimizes false alarms from cooking

Airflow: 160 CFM  Noise: 24 dBA Dimensions: 17 x 13

Compatible with up to 24 interconnected Kidde devices

BRK First Alert - SC9120B Hardwired Combination Smoke/ CO Alarm 4K It's a recessed box so[shortdesc] Alarm Type Smoke & Carbon Monoxide Power Source Hardwired Sensor Photo Electric Interconnects Yes Battery 9V [ shortdesc] The First Alert Hardwired Combination Smoke CO Carbon Alarm is built for easy installation into your homes electrical system, delivering constant protection you can count on. Even during a power outage, a built in 9V battery backup keeps your safety uninterrupted. Advanced ionization and electrochemical sensing