Traditional interaction is purposeful, but interactions based on sensing and environmental context are of lower salience and require less explicit attention. The extreme end of this spectrum, but becoming more common, is implicit interaction, which occurs when a user action intended for one purpose is interpretted to achieve some other goal. Because it is an extreme point, incidental interaction acts as a touchstone allowing us to explore the limits of traditional interaction models, task analysis, cognition and software architectures. We find that all either breakdown or require rethinking in the face of these radically novel interactions.

keywords: ubiquitous computing, contextual interfaces, sensing technology, incidental interaction