Based on ethnographic fieldwork in Japan undertaken in 2018 and 2019, this chapter invites readers to pay attention to what is going on behind the numbers produced by the network of government-installed fixed radiation monitors in Fukushima. Ostensibly they are there to monitor radiation from the Fukushima nuclear disaster, but ‘what is it for?’ Monitoring has been able to do other things like help reinstate important social practices or demonstrate care and attention. These things might not necessarily come to mind when considering what measuring and monitoring is there to do. I begin by exploring what exactly is meant by radiation measuring and monitoring, before starting to examine some of the reasons for doing it. I establish that radiation monitoring is a set of nuanced and problematic activities. The meaning of the data produced by radiation monitoring systems is open to interpretation, device failure and context. I then outline why and how radiation monitoring is different to radiation measurement and show that this difference is important but often overlooked. I then make the case for other kinds of work being done through radiation monitoring. My data suggest that radiation monitoring, whilst concerned with providing answers to questions that address immediate health concerns, also extends to marking a place as special, enabling relatively mundane things like sharing food with neighbours, selling produce or moving around different zones, as well as helping construct communities, and denoting care and attentiveness.