I used a flex sensor, which is calibrated for my back, to make a posture sensor. If the flex sensor is bent beyond a certain angle, the vibe board vibrates to let me know that my posture needs correcting. If I sit up straight, it stops vibrating.
If I had more time I would use velcro to make the lilypad and flex sensor removable so the shirt can be washed. I would also connect a button board to the lilypad which would be accessible and can be used to easily turn off the sensor whenever I want to.