A buzzer is a part of the piezo transducer as buzzer produces sound if any pressure is applied. The working is same as the above like the applied force or energy is converted into the voltage and thus that voltage result in the output.
There is a ring or we can say beep sound is commonly used in this mechanism by which you will get to know if any pressure is applied on the ring. There is no need of external force as button is the only thing you need to press it and the work will be done.
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