Hear an alarm from anywhere: If one smoke and carbon monoxide alarm detects smoke or dangerous CO levels, all wireless interlinked units will activate, ensuring the earliest possible warning. Wide coverage for full home protection: Up to 24 X-Sense Link+ devices can be interlinked to create a wireless safety network for your entire house. 2-in-1 protection: Equipped with both a photoelectric smoke sensor and an electrochemical CO sensor, this smoke alarm and carbon monoxide detector provides reliable protection against both smoke and CO. Built-in 10-year battery: Features a built-in 10-year lithium battery, so you’ll never need to worry about replacing batteries during the lifetime of the unit. Informative LCD: Displays real-time CO levels from 30–999 ppm (parts per million) taken from the surrounding air, as well as battery level and working status.