Energy reduction is one of the main challenges that countries around the world currently face, and there is potential to contribute to this by raising awareness towards sustainability in the workplace. We introduce IdleWars, a pervasive game played using smartphones and computers. In the game, workers’ proenvironmental or wasteful behaviour is reflected in their game score, and displayed through eco-feedback visualisations to try and call attention to energy wastage and potentially reduce it. A field deployment, over two weeks in a medium sized organisation, revealed that the physical and competitive elements of the game work well in engaging participants and stimulating discussion around energy wasted and conservation. However, the game turned out to encourage also some anti-conservation behaviours, as participants appropriated the game and extended its rules, sometimes in a way that favoured engagement and fun rather than proenvironmental behaviour. More in general, our study uncovered how both the game and idle time reduction in itself can rub against the daily practices of the workplace where the study was run.