Pokemon Gold & Silver To Include Walking Meter

-The PokeWalker device interfaces with your DS via infrared.
-You can transfer over a single Pokemon, who then becomes visible on the device's screen.
-As you walk around with the PokeWalker in hand, the Pokemon will gain experience.
-Its affection for you will also grow.
-The device converts your foot steps into "watts," which can be used to catch wild Pokemon and search for tools for sending back to the main Heart Gold/Soul Silver software.

Source