The Kidde Fire Sentry Smoke Alarm Micro Profile i9040E is a white, battery-operated smoke alarm with a photoelectric smoke sensor. This model, manufactured in 2017, has a 4-inch diameter and weighs 0.5 lb. It operates with a 85 dB sound rating and comes as a single unit. This alarm, designed by Kidde, is a reliable and essential component for home security against potential fires. This is a new item see pictures. Ship USPS Ground Advantage