This book is a collection of papers presented at UCS 2004, held on November 8 9 in Tokyo. UCS is a series of international symposia sponsored by the special interest group Ubiquitous Computing Systems of the Information Processing Society of Japan. The ?rst UCS was held on November 17, 2003 in Kyoto. It was held as an invitation-based symposium. UCS 2004 was the second of the series, and the ?rst submission-based conference. UCS focuses on the emerging researcharea of ubiquitous computing systems. This emergence is an outcome of the rapid evolution in smart appliances and devices, as well as...