The First Alert Atom is protection at its finest. Its micro design adds an element of style to safety. This photoelectric alarm is a fraction of the size of a standard alarm and provides all the necessary protection to help keep your family and your home safe. Its features are as follows: -Advanced Micro Technology, -Maximum Protection, Fewer false alarms from shower steam and cooking smoke, -Photoelectric Sensor which detects slow smoldering fires -Long-life Lithium Battery, -Easy Installation, -Smart Product Clip System, -Loud and Powerful Penetrating Sound