MOS Reference: UL-listed residential and commercial smoke detector providing early warning of fire conditions to allow safe evacuation. Ionization models excel at detecting fast-flaming fires with small combustion particles, while photoelectric models are more responsive to slow-smoldering fires that produce larger smoke particles. 85dB alarm horn is audible through closed doors. Test button verifies alarm and battery function. Low-battery chirp alerts when 9V battery replacement is needed. Mounting hardware and battery included. Install on ceilings or high on walls per NFPA 72 spacing requirements. Replace the entire unit every 10 years.