Universal Security Instruments 9-Volt Battery Operated Photoelectric Smoke and Fire Alarm, Model SS-901-LR Photoelectric smoke and fire alarm powered by a replaceable heavy-duty battery to ensure maximum protection Fast-and-easy installation with all mounting hardware included  No wiring required Also features a large mounting plate Features a red LED light that flashes when the alarm goes off and a cover designed to protect against contaminants Comes with a three-year limited warranty