This paper presents the uPen, a laser pointer combined with a contact-pushed switch, three press buttons and a wireless communication module. This novel interaction device allows users to interact on large displays at a distance or directly on the surface with full-function of mouse. Onboard software enable the uPen system to identify different users and provide personalized services to them, such as associating users with corresponding privileges, giving access to each participant?s private content (e.g., home pages, personal calendars). Additionally, with our two-step association method, the uPen system has the ability to distinguish strokes of different uPens working simultaneously and support multiuser simultaneous interaction. A prototype system has been implemented in our Smart Classroom [1]. And user studies show the benefit of using it.