DESC: The leading cause of accidental poisoning deaths in North America is carbon monoxide it's odorless, tasteless, and invisible. It is a silent killer. Kidde Carbon Monoxide Alarms include the most accurate sensing technology available the patented nighthawk electrochemical sensor. This unit combines a carbon monoxide and ionization smoke alarm providing two important safety devices in a single unit. This alarm includes a voice warning system that announces "fire, carbon monoxide, low battery, or smart hush activation." the voice alarm eliminates any confusion and clearly warns you and your family of a smoke or carbon monoxide danger or if your battery is in need of replacement. This unit is hardwired and will work with many interconnected systems. This combination alarm has battery backup protecting you and your family even during a power outage when many incidences occur. Install at least one carbon monoxide alarm on every floor and in sleeping areas.