As our physical environments become ever-more connected, instrumented and automated, it can be increasingly difficult for users to understand what is happening within them and why. This warrants attention; with the pervasive and physical nature of the IoT comes risks of data misuse, privacy, surveillance, and even physical harm. Such concerns come amid increasing calls for more transparency surrounding technologies (in general), as a means for supporting scrutiny and accountability. This paper explores the practical dimensions to transparency mechanisms within the consumer IoT. That is, we consider how smart homes might be made more meaningfully transparent, so as to support users in gaining greater understanding, oversight, and control. Through a series of three user-centric studies, we (i) survey prospective smart home users to gain a general understanding of what meaningful transparency within smart homes might entail; (ii) identify categories of user-derived requirements and design elements (design features for supporting smart home transparency) that have been created through two co-design workshops; and (iii) validate these through an evaluation with an altogether new set of participants. In all, these categories of requirements and interface design elements provide a foundation for understanding how meaningful transparency might be achieved within smart homes, and introduces several wider considerations for doing so.