The io Personal Digital Pen from Logitech, which looks like a futuristically designed marker-pen, incorporates an optical sensor that captures your keystrokes. Software inside the pen digitises these, turning them into information a PC can understand and display. For the pen to work in this way, you have to write on special ‘digital paper’, although its ordinary ink cartridges allow you to write on standard paper too. The digital paper incorporates an irregular grid of tiny dots, and it’s these that allow the optical sensor in the pen to do its job.