The Wii MotionPlus which was announced by Nintendo in a press release on July 14, 2008, is an expansion device for the Wii Remote video game controller that allows it to more accurately capture complex motion. It tracks players's movements in finer detail and with greater accuracy. This simple, optional attachment shall enhance the pleasure for playing the Wii.

According to Nintendo, the sensor in the device supplements the accelerometer and Sensor Bar capabilities of the Wii Remote to enable actions to be rendered identically on the screen in real time.

Features:

The Wii MotionPlus features a pass-through External Extension Connector, allowing other expansions such as the Nunchuk or Classic Controller to be used simultaneously with the device. The attachment has a color-coded mechanical slide switch for locking the clip release. When attached to the Wii Remote, the unit extends the length of the controller body by approximately 1½ inches (4 cm). Each Wii MotionPlus incorporates a longer, custom version of the Wii Remote Jacket to accommodate the added length.

References Link: http://en.wikipedia.org/wiki/Wii_MotionPlus