Over at Nintendo Gossip they claim that the release of a gyro-sensor cartridge for the DS is imminent.

The secondary expansion slot on the Nintendo DS system can currently be used for Game Boy Advance cartidges or for the rumble pack, released in October last year. An anonymous tipster has told the website that this new cartridge will fit into this slot allowing DS to be used as a controller for Wii.

The sensor will also be used for games on the DS with Tony Hawk's Downhill Jam said to be the first game to take advantage of this technology.

Apparently the cartridge will be shown at the Games Convention in Liepzig at the end of the month. We'll need to wait till then to discover whether the rumour is true.

Source : Nintendo Gossip