[petek]

Yup, they are real and they work. The electronics are based upon an accelerometer. Some simple math and you can get all sorts of information out of the accelerometer data.

Fundamentally it's all based upon the same sort of thing as the inertial guidance system on ICBMs. The neat thing is that the sensor and computer that use to fill a whole electronics bay in a missle can now fit on the top of your little finger's finger nail.