Bad posture. Ellen writes -

When in doubt of your posture just use the Bad Posture belt to get notified of your bad posture. This is enabled with an Arduino board, a Wave Shield from Ladyada, a flexi bend sensor and a push button! The bend sensor is fitted in a belt together with the rest of the electronics. By placing the bend sensor at the back of the belt I can detect when the back is arched and not. With the push button I set the desired arche of the back and “calibrate” the back and the belt to remember this value. When the back is more arched than this value the Wace Shield makes its sound!