The self-drive piezo transducer has no built-in drive circuit (passive). Still, it has a very similar structure to the external drive piezo transducer, except that a ceramic plate added a feedback electrode, and a transistor and resistor are together to form a simple oscillation circuit. When a DC voltage is applied to trigger the vibration, the sound of the product emitted by the resonant frequency preset is characterized by low power consumption and high reliability. Therefore, various alarms, anti-theft, and smoke detection widely used the self-drive piezo transducer.