This mod is called "GeneZap," and its motto is "No pity for bad players." It's a dog shock collar programmed to zap the wearer whenever he screws up or takes damage in any of half a dozen Sega Genesis games. (I'm guessing the first four letters are pronounced as two syllables, as in "Genesis," not "Gene" as in Okerlund.)
It's the creation of these two French gentlemen, who spend five zut-alors filled minutes demonstrating its torture potention on titles like Sonic the Hedgehog, Golden Axe 3, Mega Bomberman and other games, taking shock damage IRL whenever their characters take damage in-game. You can feel the tension mounting as Sonic ponders how to get by an ordinary badnik, slips off the cliff and loses all his rings, and his French-speaking player yanks at his neck and lets out a groan of agony. The best part comes at 4:10 when Sonic falls into a spike pit and bounces twice, resulting in a stream of bleeped-out French invective.
The pair posted a detailed description of their work, in case you want to, you know, build this for yourself. My favorite detail is the fact they modified Battletoads, one of the most impossible old-school video games of all time, to shock you on a loss of life, or a loss-of-life hit. What's the effect? I'll tell you what the effect is! It's pissing me off!