It is starting to look like Microsoft's Protect Natal motion interface will be a real cheap upgrade. According to Primesense, who have been making the beast, the sensor that drives Project Natal is a 'low-cost, plug and play' technology.

Primesense says on its website that the PrimeSensor Reference Design is a low-cost, plug and play, USB-powered device that can either sit on top of or next to a television screen or a monitor, or be integrated into them. “The Reference Design generates realtime depth, color and audio data of the living room scene,” the site says.

'It works in all room lighting conditions (whether in complete darkness or in a fully lit room). It does not require the user to wear or hold anything, does not require calibration and does not require computational resources from the host's processor.'

It adds: 'The PrimeSensor design includes an advanced visual data processing middleware optimized for mass-market CE products called NITE. NITE provides the algorithmic framework for the development of rich natural interaction applications.

'The NITE SDK is built to match GUI design and development on one hand, and games development on the other, by providing a fully documented API and framework.'

This all means that it should be a cheap upgrade to an Xbox 360 which could improve adoption.