The accessory, which was sold in Japan for like, two months, differed from Nintendo's E3 anti-coup, the Vitality Sensor, only in that it clipped to your ear rather than your finger. We still don't really know how Nintendo and its developers plan to use the Vitality Sensor, but the Bio Sensor could be instructive here:
In this particular title, you could have the game of Tetris either speed up or slow down as your heart rate increased. The former game mode would allow you to relax when things got too tense, and the latter would force you to control your reactions if you didn't want the game to get uncontrollably difficult.
As a sarcastic, 1998 version of me might've said: Oh, sweet.