First Alert, 9V, Photoelectric Smoke & Fire Alarm Detector, Provides Maximum Protection, Slim Design, Less Than An Inch Thick, Maximum Protection Alarm Has A Patented Smoke Entry System That Allows A Direct Smoke Path To The Photoelectric Sensor To Detect Regular & Slow, Smoldering Fires, Nuisance Free Technology Will Reduce False Alarms That Result From Cooking & Shower Steam, Includes Power LED & Alarm Indicator, End Of Life Signal & Mute & Single Test/Silence Button So You Can Test Your Alarm Regularly, Installation Is Simple With The Simple Twist Lock Wall & Ceiling Mount, Meets UL217 Standards, 10 Year Limited Warranty.