According to the principle of sounding different points:
1. Electric siren: Convert electric energy into mechanical energy, and then convert mechanical energy into sound energy.
2. Electroacoustic alarm: The audio small signal is converted into sound energy by low-frequency power amplification. That is, electrons can be converted into sound energy.
3, pneumatic alarm: the electrical energy is converted into mechanical energy, and then converted from mechanical energy to gas energy. Convert from gas energy to sound energy.
According to the setting conditions are divided:
1. Stationary alarm: An alarm installed at a fixed location.
2. Motorized alarms; alarms installed in motor vehicles or other forms used in sports.