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Abstract. Using existing communications infrastructure, such as 802.11 and GSM, researchers have demonstrated effective indoor localization. Inspired by these previous approaches, and recognizing some limitations of relying on infrastructure users do not control, we present an indoor location system that uses an even more ubiquitous domestic infrastructure-the residential powerline. PowerLine Positioning (PLP) is an inexpensive technique that uses fingerprinting of multiple tones transmitted along the powerline to achieve subroom-level localization. We describe the basics behind PLP and demonstrate how it compares favorably to other fingerprinting techniques.

We developed an inquiry technique, which we called "paratype," based on experience prototyping and eventcontingent experience sampling, to survey people in reallife situations about ubiquitous computing (ubicomp) technology. We used this tool to probe the opinions of the conversation partners of users of the Personal Audio Loop, a memory aid that can have a strong impact on their privacy. We present the findings of this study and their implications, specifically the need to broaden public awareness of ubicomp applications and the unfitness of traditional data protection guidelines for tackling the privacy issues of many ubicomp applications. We also point out benefits and methodological issues of paratypes and discuss why they are particularly fit for studying certain classes of mobile and ubicomp applications.

A person often has highly context-sensitive information needs that require assistance from individuals in their social network. However, a person"s social network is often not broad enough to include the right people in the right situations or circumstances who can satisfy the needs. The ability to satisfy context-sensitive information needs depends on a person"s ability to seek the answers from appropriate individuals, who must then provide a response in a timely manner. To gain an understanding of how to better support the sharing of information, we conducted a four-week diary study examining 20 people"s perceived daily information needs and sharing desires. We provide a structured framework for understanding the types of information people need and discuss when and how people are able to satisfy their needs. Using these findings, we discuss research and design opportunities for addressing the shortcomings of the existing information sources by connecting information altruists with an audience by leveraging weak ties through situation and circumstance, and providing a timely asynchronous connection to these sources.