The two basic types of fire alarm systems in use today are known as manual and automatic. Both manual and automatic fire alarm systems can be designed to either protect lives only or protect lives and property. Automatic fire alarm systems may operate in either a conventional or addressable configuration.
A manual fire alarm relies on an occupant of a building to discover a fire and hand activate the alarm. Devices known as call points are typically installed near doors and stairwells to activate the alarm system. This type of fire alarm is generally used in commercial or industrial buildings where no one will be sleeping. Automatic fire alarms utilize a network of sensing devices to detect the presence of fire and sound an alarm. In addition to sounding an alarm, both manual and automatic fire alarm systems can be used to activate sprinkler systems and notify the fire department.
Certain types of fire alarms are designed primarily to protect the lives of the occupants of a home or building. This type of fire alarm will sound an alarm when a fire is detected but may not activate sprinkler systems or notify the fire department. The more complex versions of this type of system will also shut down the ventilation system to prevent smoke and toxic fumes from spreading to other parts of the building. Other types of alarm systems will not only alert the occupants, but also notify firefighters and activate sprinkler systems to help contain the blaze and minimize damage to the structure.
Source: wiseGEEK at wisegeek.com