Keep your family safe with this battery operated smoke and carbon monoxide alarm; battery powered alarms provide continuous monitoring of CO and smoke levels, even if there's a power failure(Operated by 2 x 1.5V AA Batteries (not included) 2-in-1 Accurate, Reliable & Highly Sensitive Alarm: Equipped with both photoelectric smoke sensor and electrochemical CO sensor that work independently of each other; every second counts; detects both fast and slow-burning , and instantly notifies you when dangerous smoke or CO concentration is detected while minimizing false alarms; provides the ultimate protection from 2 deadly threats, all contained in 1 unit Indicator lights on the face of the unit display the presence of smoke or carbon monoxide, while an 85dB siren provides a clear, loud warning upon detection Simple to Use: Test/Silence button enables you to test the alarm weekly, and to easily silence the alarm when false alarms occur; malfunction and low battery warnings allow you to easily know the working status of the alarm; in case of an emergency, an alarm tone of over 85 dB will sound throughout your entire home, instantly alerting the entire household, even those in sleep Quick & Easy Installation with Guaranteed Quality: Product Dimensions: 4 * 4 * 1.5 inch, Requires no rewiring; easy to mount on any wall or ceiling with the included mounting bracket, screws and anchor plugs; certified to meet the UL safety standards for your peace of mind and absolute confidence in our product. you can get: 1. two detector alarms with Mounting bracket, 2. one manual, 3. four screws.