First Alert P1000. The First Alert Atom is protection at its finest. Micro design. 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. Features: advanced micro technology, maximum protection with fewer false alarms, photoelectric sensor which detects slow smoldering fires, long-life lithium battery included, easy installation with Smart Product Clip System, loud and powerful penetrating sound, 10-year limited warranty. Weighs 3 oz.