While people may think of an individual device as an independent product, the reality is that, in operation, it will be part of a complex and dynamic cyber-physical and socio-technical system. It follows that to design IoT devices, and to be confident about their reliability and safety in use, they must be considered in this context of complex coupling-which may be dynamic and ad hoc, and include accidental assembly of systems. This paper aims to facilitate this by describing different kinds of coupling that may occur in and between IoT systems, including some which often appear to be neglected. We also suggest different ways of looking at these coupled systems, including the notion of Social Machines. Finally, we suggest that behaviours evident in social media might give insight into phenomena in IoT systems, for example `fake data' by analogy with 'fake news'.