In this chapter, we focus on the so-called ‘smart home’ as an archetypal group space into which the Internet of Things is spreading. As most homes are shared spaces we focus on what ‘good data’ might look like in a space that is essentially defined by the interpersonal relations between their occupants; how good is it really, and how do we avoid it becoming ‘bad data’? We engage with this problem in two ways. First, we consider the grey area that is interpersonal data from a legal perspective, by considering transparency and accountability of smart home data, ownership and responsibilities. Second, through short narrative design fictions we speculate on how the smart home might provoke unconsidered, problematic or unexpected data practices both good and bad. We draw on these to conclude with reflections on and implications for the specific but complex challenges that designers and occupants of the modern smart home face in trying to engage in good data practices.