This sensor from SparkFun - USA
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.
VIDEO - Click Here
Resonant Frequency(kHz): 6.3 ±0.6kHz
Resonant Impedance (ohm): 1000 max
Capacitance (nF): 10.0 ±30% [1kHz]
To use it with your Arduino Board Click Here
Please note in datesheet the part number for this element is 7BB-20-6L0