27mm Piezo Electric Sensor

A piezoelectric sensor or element is a device that uses the piezoelectric effect to convert voltage to vibration and vibration to voltage. This is a piezoelectric disc that picks up sound from musical instruments and other devices. Because it produces analogue output, you can connect it to a comparator circuit to produce digital output, or you can connect it directly to the microcontroller you're using. It is small in size and reliable enough to handle any rough use, making it suitable for many types of instruments such as acoustic guitars and drums.

This piezoelectric sensor 27mm measures changes in pressure, acceleration, force, temperature or strain and converts them into electrical voltage.  This is generally used to detect vibration or a knock. This can also be usedfor a very small audio transducer such as a buzzer. This is great for acoustic guitar pickups, drum triggers and more.