Continuing trends in sensor, semiconductor and communication systems technology (smaller, faster, cheaper) make feasible very dense networks of fixed and mobile wireless devices for use in many different sensing and decision-making systems. In this paper we present the design and development of GNOMES, a low-cost hardware and software testbed. This testbed was designed to explore the properties of heterogeneous wireless sensor networks, to test theory in sensor networks architecture, and be deployed in practical application environments. We also present an overview of architectures for extending the lifetime of individual nodes in the network, along with the design tradeoffs that this presents.