The rapid development of wireless technologies,such as Bluetooth, IEEE 802.11 and IEEE 802.15.4 protocol hasallowed the deployment of wireless sensor networks withthousands of sensor devices in physical environments where theconstruction of a fixed infrastructure is inconvenient orimpossible. System designers have been facing the challenges ofusing unreliable wireless channels and limited battery power todevelop software and protocols for sensor networks. This workfocuses on the issues of robustness and efficiency in the designand implementation of wireless sensor networks using SunSPOTs device. Our implementations not only allow multiplesensor nodes to simultaneously connect to the basestation, butalso improve the robustness by handling loss of connection (dueto node movements or radio interference). To support flexibleand efficient data collection, a sensor collects data duringdisconnected status, and automatically uploads the stored datawhen it is in the range of a basestation. The testbed is useful forresearches on human mobility pattern, environmentalmonitoring, and health care, to name a few