24/7 Self-testing components are always checking the device to ensure it's operating as expected (not a substitute for a manual push test) Easy installation mounting bracket included for quick installation in 4 orientations Photoelectric sensor detects visible fire particles associated with slow, smoldering fires, while the electrochemical sensor detects carbon monoxide 85-decibel alarm LED warning indicators alert you to various status: green = normal operation, amber = operating error, and red = smoke, fire or carbon monoxide event Battery operated to provide reliable detection, even during power outages; two AA batteries included UL Listed with a 10-Year limited manufacturer warranty on the alarm only (not a battery performance claim). Warranty begins when the alarm is powered on. If that date is unknown, it should be assumed that replacement is needed.