Wireless sensor networks emerged as a key technology for prolonged, unsupervised monitoring in a wide spectrum of applications, from biological and environmental to civil and military. The sensor networks sbould operate autonomously for a long period of time under stringent resource and energy constraints. Energy consewation and power-awareness have become B focus of a number of research efforts, as sensor network nodes must operate on batteries or use energy extracted from the environment,

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... as solar energy or vibrations. Runtime power measurements and characterization of real existing systems are crucial for studies that target power optimizations, including techniques for dynamic adaptation based on the current energy status. This paper introduces an environment for unobtrusive real-time power monitoring that could be used for a number of wireless-sensor platforms. We describe our methodology for calibration and validation of the environment and give empirical data for the TeIos wireless sensor platform when it runs a subset of representative applications. I. INTRODUCTION Recent technology advances in sensors, microprocessors, and wireless communications have enabled design and proliferation of ad-hoc wireless sensor networks. These networks consist of a Iarge number of inexpensive and miniature sensors that can monitor and control environments without human intervention for a long period of time. Current research efforts aim at developing of new sensing devices, architectures for sensor platforms E1 J [2J, wireless communication protocols 131 [4] [5], as well as system support for design and evaluation of sensor networks [6] 171. Energy consumption is a first class design constraint in wireless sensor networks as they are typically battery operated. To extend each node's lifetime it is necessary to reduce power dissipation as much as possible; dissipation below 100 microwatts will enable operation on energy scavenged from the environment. Various design trade-offs between communication and on-sensor computation, collaborative protocols, and hierarchical network organization can yield significant energy savings. Once the 0-7803-8808