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.

• Resonant Frequency(kHz): 6.3 ±0.6kHz
• Resonant Impedance (ohm):  1000 max
• Capacitance (nF): 10.0 ±30% [1kHz]