Low power consumption is a critical issue in wireless sensor networks. Over the past few years, a considerable number of ad-hoc architectures and communication protocols have been proposed for sensor network nodes. If on one hand custom solutions carry the greatest power optimization potential, widespread communication standards guarantee interoperability and ease of connection with existing devices. In this paper we present a variable-granularity power model of Bluetooth, and apply it to variable-complexity optimization scenarios, to devise optimal power management policies. These policies, if backed by hardware implementations that are more power-aggressive than those available, could make the protocol fit for a wider range of sensor networks than it is today.