There was a guy a while back demonstrating a box you plug your tool into and a blade guard that had little foil tape edges to sense if you touched it. The box would do some electricity voodoo (shove DC into the motor maybe?, not sure) that would stop the blade fairly quick (2-3 seconds, iirc). He had no interest in developing the product himself - the last i saw he was trying to entice licensing or sale of the concept. The name of the product was called The Whirlwind -- something or other. Haven't heard mention of it in a few years now, though.