This demonstration is in three parts. Firstly we are showing a wearable computer built into a cycle helmet. This comprises a gumstix single board computer, an ultrasonic receiver module and a lithium polymer battery. The helmet interacts with an ultrasonic positioning system. This system requires no RF or infra-red synchronisation enabling fast and accurate performance. Lastly we are providing an interactive game based on Tux Racer with which conference attendees can appreciate the performance of the overall system.