In this paper, the authors examine the use of thin client based user terminals to realize the RFID tag based ubiquitous computing environment. The ubiquitous service targeted is not information retrieval via RFID but the user observation service based on environment perception. Thus the user terminal must ensure service consistency even when the communication link to the server is disconnected. In order to achieve this, the authors propose an event cache mechanism that stores predicted event conditions and the corresponding reactions. A prototype and evaluation results are also described.