![35mm Piezo Element](http://shops.wizrobotics.com/cdn/shop/products/35mm_Piezo_Element_{width}x.jpg?v=1562626783)
Piezo elements come in handy when you need to detect vibration or a knock. You can use these for tap or knock sensors pretty easily by reading the voltage on the output. They can also be used for a very small audio transducer such as a buzzer.
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