Large scale distributed systems comprising many administration domains have been well-researched. An example is a national health service, with domains such as primary care practices, hospitals, specialist clinics, etc. A new and relatively unexplored scenario is technology-assisted living, in which domains are small, dynamically created, and are associated with units of personal living. There is a great deal of commercial interest in providing technology to support assisted living, but services are created in isolation. We explore how such services could be integrated with a system that can ensure security and privacy. We propose to audit both system behaviour and the actions of principals, holding particular regard to the fulfilment of their obligations, to establish a computational expression of the trust to be associated with each principal.