The Kidde Hardwired Smoke & Carbon Monoxide Detector, AA Battery Backup, Voice Alerts, Interconnectable, LED Indicators, model 900-CUAR-V, is an alarm combo that detects smoke, fire, & carbon monoxide gas, using a single alarm. Operating through your home's wiring (120V AC power), while 2-AA batteries (included) provide battery backup during the event of a power failure, the Kidde Smoke and Carbon Monoxide Alarm is equipped with self-testing components that are always checking the unit to ensure the device is operating as expected*. Photoelectric sensing technology that senses visible fire particles (associated with smoldering fires), while an electrochemical sensor detects carbon monoxide. When a smoke, fire, or carbon monoxide event occurs, the Kidde fire alarm warns with an 85-decibel alarm sound & flashing red LEDs, and voice alerts announcing, "Fire! Fire!". For carbon monoxide detection, the alarm will sound with the announcement "Warning! Carbon Monoxide!". When the smoke alarm is at the end of its life span, the detector will announce, "Replace Alarm!". Three LED warning lights provide status of the alarm: a green status alerts to the alarm operating properly, amber alerts to faulty operation or connection, and red alerts to smoke, fire, or carbon monoxide. The Smart-Hush button silences the unit for approximately 8 minutes, which is helpful when this smoke detector carbon monoxide detector combo sounds from things like routine cooking or shower steam. Install a carbon monoxide smoke detector combo on every level of your home and near bedrooms to help keep your family safe. UL Certified with a 10-year limited manufacturer's warranty. *Self-testing is not a substitute for a manual push test of the alarm. Perform a button test once per week to verify proper alarm operation. **Alarms only connect with select Kidde alarms that have hardwired AC interconnect capability (see User Guide).