Finally, as part of the formative evaluation prlan research team members made a series of heuristic observations on-site to identify problems and usability issues of the proposed applications and the implemented technology. We employed observations as part of a heuristic evaluation, a usability inspection method, which refers to a class of techniques in which evaluators examine an interface for usability issues. Observation is considered an informal method of evaluating usability because observers rely on heuristics along with their experience and the knowledge. The observation sessions were also useful in validating the sensor technology. During these sessions residents were asked to carry out certain activities (for example, meal preparation) while being observed by two research assistants who made notes and timed tasks using a portable data assistant (PDA). The notes were compared with the sensor data to validate the collected data sets. Furthermore, the observations aimed to identify whether the installed technology becomes obtrusive during regular daily activities in the home.