Baby wearable technologies are becoming increasingly popular, particularly in early infancy. However, little research has been conducted to investigate how baby wearable technologies are adopted and used in parenting. This paper presents a two-week in-depth situated study with six mothers in their homes consisting of contextual entry and exit interviews, video recordings of "out-of-box" experiences, and a diary study. Using interpretative phenomenological analysis, participants' use and expectations of the baby wearable technology were examined. Use of the device directly impacted upon parents' knowledge production and anxiety, and influenced the perceived physicality and social factors of parenting. We frame these findings around sociological norms of the vulnerable child and responsible mother, as well as the notion of "lived informatics", where individuals' interaction with the technology influenced the perception, use and impact of the baby wearable on everyday parenting practices and familial relationships.