Chris Harrison has done some research on using scratching as an input device. In this video he demonstrates how simply scratching a wall or a desk could have some simple and inexpensive applications. Could you imagine controlling your room lights by scratching anywhere on the wall in the room you want to control? Or a coffee table that has a sensor so that you could use it to control your audio system?"We present Scratch Input, an acoustic-based input technique that relies on the unique sound produced when a fingernail is dragged over the surface of a textured material, such as wood, fabric, or wall paint. We employ a simple sensor that can be easily coupled with existing surfaces, such as walls and tables, turning them into large, unpowered and ad hoc finger input surfaces."Via: Procrastineering