Visual version, avoids disturbing coworkers

  brew install screenbrightness
  while true; do sleep 1800; brightness 0; sleep 0.1; brightness 1; done

Or, in powershell (sans sox),

     while($true){(New-Object Media.SoundPlayer "C:\YourPreferredSound.wav").Play(); sleep 1800;}

I'm using the Single Hit Tibetan singing bowl from: http://www.sound-effects-hunter.com/tibetan-bowl-sound/

Does this help you mentally? What changes have you seen since starting this 'mindfulness' practice?

I'm hesitant to say anything about mental effects, since I'm far from able to objectively measure such things, especially since I haven't been keeping any kind of measurements or records. But it certainly keeps me from slouching quite as much.