The BRK SCO2B has both ion and electrochemical sensors with optipath 360 technology - patented technology providing 360 degrees of direct access to the smoke sensor. Ionization technology works best at detecting small particles, which tend to be produced in greater amount by flaming fires. Electrochemical sensing is the most advanced sensing in CO technology. This product offers two silence features for silencing unwanted alarms as well as silencing low battery chirps and allows offered latching to help indicate which unit went into alarm. A 9 V alkaline battery is included with this product and offers a 7-year warranty. *