Flex (bend) sensor 4,5"
This sensor can detect 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 ~10KΩ. When flexed all the way the resistance rises to ~20KΩ. They're pretty similar to FSRs so following this tutorial will get you started (link to Adafruit).