First Alert Smoke Detector and Carbon Monoxide Detector Alarm | Hardwired with Battery Backup, BRK SC9120B Keep your family safe with this hardwired smoke and carbon monoxide alarm; the battery backup means constant monitoring, even if there's a power failure Features an electrochemical Carbon Monoxide sensing technology as well as an ionization sensor that detects the fine particles of a fast-burning fire Indicator lights on the face of the unit display the presence of smoke or carbon monoxide, while an 85-decibel siren provides a clear, loud warning upon detection Can connect to other compatible BRK or First Alert detectors, to ensure all alarms will sound when threat is detected Simple to use, with a single test/silence button, and side-load battery compartment; tamper-resistant locking brackets and universal mounting brackets make installation easy Rigorously tested to meet UL standards