Gabrys’s How to Do Things with Sensors critically examines citizen-sensing technologies by treating sensors not as neutral instruments of environmental measurement, but as devices that organise particular forms of action, citizenship and political imagination. The text begins from the proliferation of how-to guides, tool kits and DIY digital cultures, arguing that these instructional formats do more than teach technical assembly: they shape what becomes thinkable, doable and governable. In citizen-sensing projects, the “sensing citizen” is imagined as an instrumental actor, technically equipped to monitor pollution, generate data and intervene in policy. Yet Gabrys complicates this promise by showing that sensors rarely produce straightforward empowerment. They require calibration, maintenance, platforms, data interpretation, comparison with regulatory standards, community organisation and political translation. The case of air-quality monitoring is especially revealing: low-cost sensors may appear to democratise environmental evidence, but they also expose inequalities in who can sense, whose data count, and whose environmental claims become credible. Gabrys therefore proposes open-air instrumentalism, a pragmatist and feminist reworking of instrumentality in which tools do not simply deliver predetermined outcomes, but open contingent relations among technologies, environments, publics and regulatory systems. Her notion of the sensor tool kit as a flat-pack cosmology is particularly incisive: tool kits assemble worlds by defining relevant components, users, problems and effects, while often concealing the social and political assumptions built into their instructions. Rather than rejecting sensors, Gabrys argues for retooling them: using breakdowns, workarounds and situated practices to expand environmental participation beyond technical functionality. The book’s central contribution is thus to show that doing things with sensors also means doing things with citizenship, evidence, pollution and collective life; environmental monitoring becomes a technopolitical practice whose value lies not only in data production, but in the more just worlds that may be experimentally composed through it.