Konami has released Boktai, a GameBoy game with a solar sensor that uses sunlight to alter gameplay.

According to the publisher, the game has a solar sensor built into the GBA cartridge. Certain monsters can only be destroyed by harnessing sunlight. According to game reviewer Gene Emery, artificial light isn't good enough; the cart required real sunlight. Vampires and other monsters in the game flourish at night, so the physical location of the player has a direct result on the game.

What I find most interesting about this game is the direct impact of the physical world on the gameplay. The gameplay depends on specific action by the player in the material world. In the past, I've tried to create this kind of action in advergames, where the player has to buy something or provide information to upgrade a character, advance a level, or recover from a lost life. The problem with this strategy is that it's completely arbitrary; the required real-world actions have absolutely nothing to do with the gameplay, and so they often fail. Playing in sunlight is somewhat arbitrary too, I suppose, but the point is that there is a continuity between material-world action and game-world action. That's the key.

And I suppose it's not just a little ironic that the game actually gets its players out of the house.