Over the last few years the availability and accuracy of all types of sensors has increased many times over. Whether it's accelerometers, ultra-sonic range finders, digital compasses, or even fully fledged inertial measurement units (IMUs) there's never been a greater choice.

Many sensors are extremely small and lightweight, and can easily be placed into hostile environments with only small amounts of protection.

Particularly exciting are the growing number of 'biometric' sensors that can interpret fingerprints, retinas, or other biological indicators.