A Statistical Reasoning System for Medication Prompting -- Tracking Free-Weight Exercises -- Playful Tray: Adopting Ubicomp and Persuasive Techniques into Play-Based Occupational Therapy for Reducing Poor Eating Behavior in Young Children -- Privacy Enhancing Technologies for RFID in Retail- An Empirical Investigation -- Ninja: Non Identity Based, Privacy Preserving Authentication for Ubiquitous Environments -- Field Deployment of IMBuddy: A Study of Privacy Control and Feedback Mechanisms for Contextual IM -- Yours, Mine and Ours? Sharing and Use of Technology in Domestic Environments -- How Smart Homes Learn: The Evolution of the Networked Home and Household -- "My Roomba Is Rambo": Intimate Home Appliances -- Symbolic Object Localization Through Active Sampling of Acceleration and Sound Signatures -- An Exploration of Location Error Estimation -- Security by Spatial Reference: Using Relative Positioning to Authenticate Devices for Spontaneous Interaction -- Users and Batteries: Interactions and Adaptive Energy Management in Mobile Systems -- An Empirical Study of the Potential for Context-Aware Power Management -- Amigo: Proximity-Based Authentication of Mobile Devices -- At the Flick of a Switch: Detecting and Classifying Unique Electrical Events on the Residential Power Line (Nominated for the Best Paper Award) -- An 'Object-Use Fingerprint': The Use of Electronic Sensors for Human Identification -- Key Generation Based on Acceleration Data of Shaking Processes -- "Merolyn the Phone": A Study of Bluetooth Naming Practices (Nominated for the Best Paper Award) -- Why It's Worth the Hassle: The Value of In-Situ Studies When Designing Ubicomp -- Locating Family Values: A Field Trial of the Whereabouts Clock -- Safeguarding Location Privacy in Wireless Ad-Hoc Networks.-Haggle: Seamless Networking for Mobile Applications -- Exploiting Social Interactions in Mobile Systems -- Rapidly Exploring Application Design Through Speed Dating -- Addressing Mobile Phone Diversity in Ubicomp Experience Development -- Sensor Networks or Smart Artifacts? An Exploration of Organizational Issues of an Industrial Health and Safety Monitoring System -- A Long-Term Evaluation of Sensing Modalities for Activity Recognition -- Cooperative Augmentation of Smart Objects with Projector-Camera Systems.

The Ubiquitous Computing conference series provides the premier forum in which to present original research results in all areas relating to the design, implementation, app- cation and evaluation of ubiquitous computing technologies. It is a well-established platform to introduce and discuss research that enables new capabilities, appropriate security and privacy, improved user experiences and simplified and powerful devel- ment and deployment practices. These proceedings contain the papers presented at the Ninth International Conf- ence on Ubiquitous Computing (UbiComp 2007) in Innsbruck, Austria, in September 2007. Our call for papers resulted in 150 submissions, each of which was assigned to a primary and a secondary member of our Program Committee. Every primary and secondary member was responsible for assigning one or more additional qualified reviewers with specific expertise in the field. After double-blind reviews and an online discussion, we had a two-day face-to-face meeting with 38 of the 40 Program C- mittee members attending the PC meeting held just before the Pervasive 2007 conf- ence in Toronto, Canada, in May 2007. We are grateful to Khai Truong , Jeremy Knight and Alex Varshavsky of the University of Toronto for providing facilities and support for this meeting. At the PC meeting, about 80 of the submissions were in- vidually and extensively discussed in one of the three subgroups sensors, experiences and systems as well as in the calibration and decision panels. The PC finally selected 29 papers for publication in these proceedings.