This sensor can detect flexing or bending in one direction.
These sensors are easy to use, they are basically resistors that change value based on how much their flexed. If they're unflexed, the resistance is about ~25KΩ. When flexed all the way the resistance rises to ~100KΩ. They're pretty similar to FSRs so following this tutorial will get you started. You can use an analog input on a micro-controller (with a pullup resistor) or a digital input with the use of a 0.1uF capacitor for RC timing.

The bottom part of the sensor (where the pins are crimped on) is very delicate so make sure to have strain relief - such as clamping or gluing that part so as not to rip out the contacts!
Dimensions:
Length: 77.57mm/3.054in
Width: 6.41mm/0.2525in
Thickness: 0.48mm/0.019in
Weight: 0.27g/0.0095oz