Recent rapid technological developments have led to the development of tiny, low-power, low-cost sensors. Such devices integrate sensing, limited data processing and communication capabilities.The effective distributed collaboration of large numbers of such devices can lead to the efficient accomplishment of large sensing tasks. This talk focuses on several aspects of energy efficiency. Two protocols for data propagation are studied: the first creates probabilistically optimized redundant data transmissions to combine energy efficiency with fault tolerance, while the second guarantees (in a probabilistic way) the same per sensor energy dissipation, towards balancing the energy load and prolong the lifetime of the network. A third protocol (in fact a power saving scheme) is also presented, that directly and adaptively affects power dissipation at each sensor. This “lower level” scheme can be combined with data propagation protocols to further improve energy efficiency.