The Kidde Smart Smoke & Carbon Monoxide Detector, WiFi, Alexa Compatible Device, Hardwired w/Battery Backup, Voice & App Alerts, 2 Pack, model P4010ACSCO-WF, uses photoelectric sensor technology to detect visible fire particles, associated with smoldering fires, and alerts you by sounding an 85-decibel alarm with voice alert announcing "Fire! Fire!" or "Warning! Carbon Monoxide!". The Kidde smart hardwired combo alarm connects to your home's wiring using standard 120V AC power voltage and provides battery backup in the event of a power failure. The built-in lithium battery backup lasts the 10-year life of the alarm, so you'll have the benefit of never having to replace a battery. Update-to-date, real-time notifications are provided through the Kidde app, so your family & friends - even the pet sitter - can monitor your home's air quality & received alerts to smoke or CO presence, high humidity levels that can lead to mold, unexpected high or low temperatures, or Total Volatile Organic Compounds (TVOCs). Setup is easy: simply download the Kidde app and scan the QR code at the back of the combination alarm. You can also use voice commands to check the connection & status of carbon monoxide or air quality by pairing it with your Amazon Alexa, Google Home, and select iPhone & Android smart devices. The LED ring-light indicator alerts you to the unit's operational status: red = a smoke, fire, or hazard, amber = operating error, and green = normal operation. The Test-Hush button silences temporary nuisance alarms, tests if the unit is operating properly, and silences a low battery or end-of-life chirp (up to 24 hours at a time for a maximum of 7 days). Install a smoke & carbon monoxide combination detector on each level of your home and inside and outside each bedroom. The Kidde smoke & CO detector is capable of hardwired interconnection to other select Kidde alarms for whole-home activation – when one alarm sounds, they all do**. UL Listed with a 10-Year limited manufacturer warranty on the alarm only (not a battery performance claim). Warranty begins when the alarm is powered on. If that date is unknown, it should be assumed that replacement is needed.**Alarms only connect with select Kidde alarms that have hardwired AC interconnect capability (see User Guide).