Passive RFID technology and unobtrusive Bluetoothenabled active tags are means to augment products and everyday objects with information technology invisible to human users. This paper analyzes general interaction patterns in such pervasive computing settings where information about the user's context is derived by a combination of active and passive tags present in the user's environment. The concept of invisible preselection of interaction partners based on the user's context is introduced. It enables unobtrusive interaction with smart objects in that it combines different forms of association, e.g. implicit and user initiated association, by transferring interaction stubs to mobile devices based on the user's current situation. Invisible preselection can also be used for remote interaction. By assigning phone numbers to smart objects, we propose making this remote user interaction with everyday items as easy as making a phone call. We evaluate the suitability of the proposed concepts on the basis of three concrete examples: a product monitoring system, a smart medicine cabinet, and a remote interaction application.

We would like to acknowledge and thank several individuals who have helped develop the CHOICE network. In particular, Anand Balachandran, and Srinivasan Venkatachary are two of the original designers and implementers of PANS. Stephen Dahl helped us deploy the network at the Crossroads Mall; Pierre De Vries handled the legal formalities and helped us with usability issues while being our liaison with the product groups Paul Hoeffer designed our web interaction. We also thank Prof. Dave Johnson of Rice University, and Prof. Mary Baker of Stanford University for the well appreciated constructive discussions.