In one of my previous post I presented a simpe handheld POV device, it was a little bulky not really suited for a true handheld device. If you are interested of building a similar gadget this is the thing you need, small enough to be mounted under your wrist watch and has a mercury switch to synchronize the display to the movement.
The entire project is open hardware, even the gerber files are available, very nice indeed. Although the pcb’s will be hard to replicate because of the small size and smd components, but not impossible.
My choice would be to redesign the pcb for an ankle mounted POV, that way the pcb could get bigger, there will be room for larger batteries, and if you make two of them you can use it instead of ankle weights when jogging or at fitness trainings.