You are sure to mistake Sigma SGM2 mouse for an oversized hearing aid. It is basically useful as a presentation device as it locks between your index finger allowing you to control the roller with your thumb, it also has a scroll wheel and a double click key which is activated by the index finger. It offers a resolution of 400/800dpi and connects via USB too bad it is not cordless as no one would want an extra wire dangling around. The mouse is compatible with Windows XP only.
The Sigma SGM2 measures 58×84×64mm and weighs 97 grams. It will be available by December in Japan for 3,480 Yen ($ 30)