I really should have chased this further when I was looking into it 8 years ago. Is really easy tech, in principle. The sensors are cheap and easy to DIY and th

I really should have chased this further when I was looking into it 8 years ago. Is really easy tech, in principle. The sensors are cheap and easy to DIY and the signal analysis isn't too hard as long as you have the sensors aligned well, which is the major issue for making a generic device, really.