With this Google Nest Protect V2 Battery 4-Pack, you will always be informed about smoke or carbon monoxide levels in your home, no matter where you are. The package includes 4 detectors that you can install throughout your house. You connect them to the Nest app on your smartphone or tablet. When a detection occurs, the Nest alerts you with a spoken alarm of 70 decibels. A voice will tell you exactly where the danger is located. The app also keeps you updated on battery status and sensor activity. The green light will illuminate as soon as the motion sensor detects movement in the dark. Each Google Nest Protect V2 operates on 6 AA batteries (included).