NFPA 72 is the comprehensive standard for fire alarm and emergency communication systems. Fire alarm systems consist of initiating devices (manual pull stations and automatic detectors) connected to a control panel that monitors the building and triggers alarm signals. Manual pull stations must be installed at accessible locations near exits, with maximum travel distance of 200 feet between stations. Automatic detectors include heat detectors (activated by elevated temperature), smoke detectors (activated by combustion particles), and flame detectors (activated by infrared radiation from flames). Smoke detectors in residential buildings must be interconnected so activation of one detector triggers alarms throughout the dwelling. Control panels monitor detector circuits continuously and must display the location of any activated detector. When a detector is triggered, the control panel activates audible and visual alarms and may notify monitoring centers. Notification appliances including horns, strobes, and speakers must be sized and positioned to ensure that alarms are audible and visible throughout the building. In office buildings, alarm signals must reach 75 decibels at least 10 feet from the appliance. Voice evacuation systems allow occupants to receive instructions and guidance during emergencies. Backup power must sustain system operation for at least 24 hours on standby and 5 minutes during alarm condition. Systems must be tested regularly and maintained by certified technicians.