Gentex 9120 Smoke Alarm, 120V AC Photoelectric w/Battery Backup & Solid State Sounder 120VAC and 220VAC with 9VDC battery back-up Low or missing battery indicator 9VDC alkaline battery included Patented three-position test switch Includes 90db piezo solid state non-latching horn Tandem connection up to 12 units; 6 on relay models Nominal 3.0% sensitivity 5:1 signal-to-noise ratio Pulsing LED sensing chamber Fully insect screen Solid State LED condition indicator Quick-disconnect wiring harness Mounting hardware adapts to standard junction boxes Protective high air velocity gasket