The fire protection system can be divided into automatic fire alarm system and linkage system according to their functions. The former's function is to send out sound and light alarm signals and indicate the location of the fire alarm after discovering a fire, making it easier to extinguish; The latter's function is to automatically start various devices after the fire automatic alarm system detects a fire, avoiding the spread of the fire until it is extinguished. From their different functions, it can be seen that they are inseparable. In fact, many fire automatic alarm systems also have the function of automatic linkage systems.

　　The automatic fire alarm system generally consists of two main parts: a fire detector and a fire alarm. Fire detectors are installed on site to monitor for any fire incidents; The fire alarm is installed in the fire control center and manages all fire detectors. When a fire alarm is detected, an audible and visual alarm signal is issued to notify the on duty personnel. Some fire alarms can also activate the linkage equipment to extinguish the fire. Some fire detectors have sound and light alarm devices that can be used without fire alarms and are generally used in households.

The principle of fire detector detecting fire occurrence is to detect the change of a certain physical parameter before and after the fire occurs. For example, detecting temperature. When the temperature rises, it can be concluded that a fire has occurred. Generally, the occurrence of a fire is determined by detecting changes in three physical parameters: smoke concentration, temperature, and light. From this, fire detectors can be divided into smoke detectors, temperature detectors, and flame detectors. In actual use, there are more of the first two.

Smoke detectors detect changes in smoke concentration on site to determine if a fire has occurred; The temperature detector detects changes in the on-site temperature and determines whether a fire has occurred; The flame detector detects changes in the spectral intensity of infrared or ultraviolet light to determine whether a fire has occurred. Smoke detectors include ion smoke detectors, photoelectric smoke detectors, and infrared beam detectors. Temperature detectors include fixed temperature detectors, differential temperature detectors, differential fixed temperature detectors, and cable type fixed temperature detectors. Flame detectors include infrared flame detectors, ultraviolet flame detectors, and composite flame detectors. Nowadays, some fire detectors are composite detectors that can test not only one physical parameter, but also multiple parameters to determine whether a fire has occurred.