These systems generally use smoke, heat or flame detectors to detect the outbreak of fire and to alert building occupants and the fire brigade. Manual call points which allow an occupant who discovers fire to raise the alarm may also be included in the system..

Single station residential smoke alarms, as installed in most homes, are the simplest system for detecting a fire and warning the building occupants.

The time between the outbreak of fire and the commencement of firefighting is the single most important factor in fire control and can be effectively reduced by having the system monitored directly by the fire brigade.

Fire alarm systems must be heard by the building occupants in all parts of the building. To achieve this, they are often connected to occupant evacuation warning and intercommunication systems which sound a defined "beep - beep - beep" throughout the building when the detection system has been activated.

Sometimes these systems automatically close smoke and fire doors, operate flashing warning lights, stop air-conditioning systems or alert critical staff via personal pagers. Today these systems extensively rely upon computer systems and are changing at the same rapid pace as is computer technology. Today's systems can be "intelligent" defining exactly where the fire is, determining if the smoke is from a fire threat or just burnt toast and advising the maintenance manager when the detector needs cleaning or other routine maintenance work is required.