The USB Posture Alert Reminder will stop you leaning in and slouching in front of your monitor. Ultrasonic sensors will detect how close you’re sitting to the infernal machine and you can choose to be reminded with red and blue LEDs. If you’re truly a masochist there’s also a warning chime but thankfully it can be turned off. It’s all powered by USB so just pop it on top of your monitor and plug it in. Around US$24.
Posture Alert Reminder is your smart companion that reminds you with flashing LEDs and chimes once you are closer than the recommended visual distance ( 35cm-60cm ) from the monitor.