PC Review posted a review on the A4Tech Wireless Battery-Free Optical Mouse

Now for the explanation of the wireless and battery-free gimmick and this should be fun, because you can do this at home! First, consider a standard wired USB optical mouse. Next, take a big knife to this imaginary mouse and cut out all the USB connectivity bits. Then stick all those into a small but shiny mouse pad. What you end up with is a USB mouse mat and a wireless mouse. The mouse draws all its power from the pad through the magic of electromagnetic induction. As long as the mouse is kept in close proximity to the pad, it should work. This is , essentially what A4-Tech have done, and by just focusing on the mouse and ignoring the fact that you have to use its special pad with it, they can say that it's the world's first wireless battery-free input device. Clever eh?

A4Tech Wireless Battery-Free Optical Mouse