Pervasive Computing : Second International Conference PERVASIVE 2004 Linz Vienna Austria April 21 23 2004. Proceedings This book constitutes the refereed proceedings of the Second International Conference on Pervasive Computing PERVASIVE 2004 held in Vienna Austria in April 2004. The 26 revised full papers presented were carefully reviewed and selected from a total of 278 submissions. The papers are organized in topical sections on activity recognition context computing near body interfaces software sensors security architectures and systems algorithms and new interfaces