The First Alert P900 smoke and fire alarm provides maximum protection and has a new sleek, slimmer design, which adds an element of style to safety. The P900 has a modern, thin square design that's less than an inch thick (half the size of a standard alarm), while still providing all the protection you need to keep what matters most safe and secure. The P900 maximum protection alarm has a patented smoke entry system that allows a direct smoke path to the photoelectric sensor to detect regular and slow, smoldering fires.