At the Heart of the Wii, Micron-Size Machines - New York Times

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The controllers communicate with the Wii console, a $250 box no larger than a child’s lunchbox, with the wireless technology known as Bluetooth. It is the means commonly used to link cellphones with their wireless headsets. The Wii remote also uses infrared, the same technology that links television sets with their remote controllers, to track where the controller is pointed.

Source: At the Heart of the Wii, Micron-Size Machines - New York Times