In this paper, the authors describe in details Unified Modeling Language (UML) modeling of login procedure, which is a part of user bar code reader application, developed for large stores and intended for use as a customer support during the shopping session. Login procedure is realized within access control system, in this case over a wireless network. Paper gives the whole modeling and implementation cycle of login procedure, from use case diagrams to the Java source code. Login procedure is modeled using interaction overview diagram, new in UML 2.0, which gives concise representation and divides complex sequence diagram into several smaller. The link between these diagrams is modeled with OCL post condition and precondition expressions.