Some functions in ambient assistance systems are enabled by sensors gathering data from the surroundings. While many prototypes are developed to prove technical concepts, for creating an acceptable, usable product additional facets need to be considered. Therefore, we present an approach to develop a functional ubiquitous system to support the monitoring and assistance of elderly family members. Besides the necessary technical concepts, insights from trust, law and user interface design are incorporated in this approach. The main idea of the approach is to deduce functional requirements from normative guidelines, theories or laws, and to combine the contributions from the involved disciplines developing the Senior Monitor demonstrator.