What you see above was recently introduced by Nintendo during their E3 presentation, the Wii Vitality Sensor.

What this peripheral essentially is, is a heart rate monitor that you attach to the bottom of the Wii controller just like you would the Nunchuk attachment. Nintendo says this attachment will “expand the appeal of video games” and sense a players pulse along with “a number of other signals being transmitted by their bodies, and will then provide information to the users about the body’s inner world.”

So, exactly waht they will be using this attachment for? Not a clue but knowing Nintendo they will probably come up with something good.

Read (Kotaku)