Photo 1—My Silicon Wallet fits in a small plastic box the size of a cigarette pack. Most of the space is required for the Cypress Invention Board, batteries, and the standard LCD module—all of which are wired point-to-point. You can reduce the size even more if you use a dedicated PCB, a miniature LCD, and SMT parts. The volume wheel on the top enables you to enter the secret code and subsequently scroll through the data pages. The light sensor is on the backside.