A fascinating project is currently looking for support over on kickstarter. Phree™ is the world’s first unrestricted, high resolution, write-virtually-anywhere mobile input device. In a nutshell, Phree lets you write, draw, annotate, and express yourself in countless other ways on virtually any surface.
Phree in action!
So how does it work? According to the developers OTM Technologies:
The patented OTM sensor is a compact 3D laser interferometer. It tracks the relative motion of a nearby surface by measuring the interference signal between a laser beam projected on the surface and the reflections from the surface. The beauty of this system is that it extracts the motion signal optically. The signal is then translated to X-Y-Z motion information by our signal-processing algorithms running on a very small, integrated electronics component.