The first alert SC9120B combination smoke/carbon monoxide alarm is perfect for protecting your family against the dangers of fast-burning fires. Hardwired directly into your home’s electrical system, this model also comes with a backup, 9V battery intended to provide emergency power in the event of power outages. The BRK SC9120B harnesses the power of the most accurate electrochemical carbon monoxide sensor, and combines that with best-in-class ionization technology.