A physical icon, or phicon, is a real object that is used to interact with a digital environment or represent some piece of digital information inside a computer. The term is used in the field of tangible computing, specifically when speaking of tangible user interfaces (TUIs). Like a traditional digital icon that is displayed on a computer monitor and can be clicked, dragged or otherwise interacted with, a physical icon is designed with the same concept in mind, except the phicon is manipulated with the hands instead of with a keyboard or mouse cursor. Ideally, a phicon could be used in a natural way inside an integrated digital environment and not necessarily be immediately recognizable as a piece of computer hardware. Although there is some research into the development and use of a physical icon and tangible computer systems, there are no consumer products or commercially manufactured systems available as of 2011.
The concept of a physical icon is to endow objects within a physical environment, such as an office, with significance in relation to a tangible computer system. For the physical icon to operate, it must be used in conjunction with a computer system that has an awareness of different external objects so it can react appropriately. The object could be used to work with a visual system that has a computer display monitor, or it could be used to interact with a non-visual system such as voicemail or a thermostat in a home.
A completely hypothetical example of using a physical icon would be in an office setting where a tangible computer and monitor are integrated into a desktop. To open a word processor on the tangible computer, a phicon such as a pen could be brought into a certain area of the desktop. The pen would trigger the computer to open a word processor and also might double as an input device. Once a document was done being written, a phicon such as a paperclip could be placed on top of the display of the document to order the tangible computer to print it. This relies on different phicons being specifically designed with some type of signal ingrained in them for the computer to receive, or it might involve a system of optical shape recognition to know what objects are being introduced.
Another area of research is creating a physical icon that, instead of simply being a representative device for human-computer interaction, actually has some type of storage or processing power of its own. This would mean that a document or program could be stored on a phicon, and that phicon could be used in the same way on any tangible computer. A physical environment ultimately could contain several networked tangible computers that are integrated into different types of objects. In this scenario, a tangible computer component could look like a small paperclip bin and the physical icon could be a paperclip, so when a paperclip is dropped into the bin, a schedule or calendar is shown on a display.