Global Positioning System - GPS - devices have become everyday items to many of us as their cost has fallen.

These devices communicate with geostationary satellites, which tell the device, exactly where on Earth it is. The potential applications for this knowledge are endless. If you know where you are, where you were and the time in between then you know your speed exactly. If you know where you are then others do too.

GPS systems can be installed in cell phones as well as satellite phones. Sportsmen and women can use GPS devices to calculate how far they have run or paddled, their current speed and average speed.

Increasingly companies are fitting them in their vehicles. Trucks may be carrying $500,000 worth of goods, so it's worth installing a GPS system so you know where it is. A similar system is sold as a theft deterrent to private drivers.

Other companies are fitting a system that interfaces with the engine management computer on vehicles in their company fleet. As a driver goes out of a predefined area, the engine power drops and continues to drop the further outside the designated area the vehicle is. The system soon pays for itself in reduced levels of unauthorized mileages.

GPS devices are now so miniaturized that they can be worn on the wrist, like a watch. GPS navigation systems are commonly fitted in trucks and delivery vans. The built in software interprets the GPS information into a series of spoken commands, like 'Turn Left' or 'You've missed the turning, take the next right and turn around'. A GPS system means that courier companies can achieve faster deadlines because drivers never get lost.