Ambient Assisted Living systems aim at providing automated support to humans with special needs. Smart Homes equipped with Internet of Things infrastructure supporting the development of Ambient Intelligence which can look after humans is being widely investigated worldwide. As any IT based system, these have strengths and also weaknesses. One dimension of these systems developers want to strengthen is security, eliminating or at least reducing as much as possible potential threats. The motivation is clear, as these systems gather sensitive information about the health of an individual there is potential for harm if that information is accessed and used by the wrong person. This chapter starts by providing an analysis of stakeholders in this area. Then explains the IoT infrastructure used as a testbed for the main security analysis methods and tools. Finally it explains a process to assess the likelihood of certain vulnerabilities in the system. This process is mainly focused on the design stage of a system. It can be iteratively combined with development to inform a developing team which system architectures may be safer and worth given development priority.