The unit shall be capable of self restoring. A screened sensing chamber to prevent entry of small insects thereby reducing the probability of unwanted nuisance alarms. Powered by 120 V AC, 60 Hz and have a monitored 9V battery backup (model 9120BA only). A visual LED (green) power-on indicator to confirm unit is receiving power. A visual LED (red) power-on indicator to confirm unit is working properly. A test button to check all alarm functions by stimulating the chamber to simulate a smoke condition, causing the unit to alarm. A solid state piezo horn rated at 85 dB minimum at 3 m. The unit shall be capable of operating between 4°C (40°F) and 38°C (100°F) and relative humidity between 10% and 90%. The unit shall center mount to any standard electrical junction box up to 4 inches diagonally without screw removal and shall be listed for wall or ceiling mounting.