The iPosture is a small white disk that you stick somewhere on your body. When it senses that you’re sitting with bad posture for more than one minute, it reminds you with a buzz to straighten up. The website specifies that the tilt sensor has a resolution of three degrees.
This reminded me that during piano lessons as a young kid, when my teacher saw me slouch she would run her nail along my back to make me sit up. Which, if you think about it, is also a form of tactile feedback for posture correction.