In this paper, we develop the concept of smart home devices as ‘invisible witnesses’ in everyday life. We explore contemporary examples that highlight how smart devices have been used by the police and unpack the socio-technical implications of using these devices in criminal investigations. We draw on several sociological, computing and forensics concepts to develop our argument. We consider the challenges of obtaining and interpreting trace evidence from smart devices; unpack the ways in which these devices are designed to be ‘invisible in use’; and reflect on the processes by which they become domesticated into everyday life. We also analyse the differentiated levels of control occupants have over smart home devices, and the surveillance impacts of making everyday life visible to third parties, particularly the police.