This basic piezo sensor from Measurement Specialties is often used for flex, touch, vibration and shock measurements.
A small AC and large voltage (up to +/-90V) is created when the film moves back and forth.
A simple resistor should get the voltage down to ADC levels.
Can also be used for impact sensing or a flexible switch.

Comes with solderable crimp pins.

Features:

• Flexible PVDF Piezo Polymer Film
• Wide dynamic range
• Laminated for higher voltage output
• 0.1" breadboard friendly leads

Documents:

• Datasheet (LDT0-028K)
• Technical manual