NFPA 72 Chapter 18 addresses notification appliances used to alert building occupants of fires. Audible notification includes horns producing 75-95 decibels at occupied areas. Visual notification includes strobe lights with 1 Hz or 2 Hz flash frequency. Combined horn/strobe appliances are most common. Strobes must be visible from key locations, with intensity scaling based on room size. Voice systems provide intelligible speech for emergency instructions. Voice system microphones allow staff to speak to occupants. Some systems automatically pre-record messages. Occupants with hearing impairments rely on visual alarms, while occupants with vision impairments rely on audible alarms. Both types must be provided in public buildings.