The PicoRadio project strives to develop the range of technologies necessary for the realization of ultralow energy wireless sensor networks. These include the study of multi-hop networks, and media-access layers that support low variable-rate data transmission while ensuring energy-consumption levels that are close to the theoretical limits. The target is to create a node that consumes 50-100 uW to operate. This power consumption would allow it to power itself from the energy sources of the operating environment.