The FIRST ALERT BRK SC9120B hardwired combination smoke and carbon monoxide alarm uses an electrochemical carbon monoxide sensing technology and ionization sensor for smoke detection. It includes a 9 V battery for continued function in the event of a power outage and it features a test/silence button, tamper-resistant locking brackets and a universal mounting bracket. This carbon monoxide smoke detector can be connected to other compatible BRK and FIRST ALERT hardwired smoke and carbon monoxide detectors. Its latching alarm indicator automatically identifies which unit initiated the alarm even after the conditions that set off the alarm have subsided.