The Visomate Vision and Posture corrector does just that. This USB device sits atop your display and will monitor your posture and vision. It will flash an LED if you are sitting incorrectly and also does the same when you are too close to the monitor. It retails for $26 and I may have to invest in it. I spend the majority of the day in front of the computer, half of the time I'm hunched over the keyboard, the other half I'm slouching and I know I'll be kicking my own ass at the age of 40 if I don't fix this now.