In this paper we develop a novel approach to conserving energy in battery powered communication devices. There are two salient aspects to this approach. First, the battery powered devices move through multiple, progressively deeper, sleep states in a predictable manner. Nodes in deeper sleep states consume lower energy while asleep but incur a longer delay and higher energy cost to wake up. Second, the nodes are woken up on demand through a paging signal. To awaken nodes that are in deep sleep, the paging signal has to be decoded using very low power circuits such as those used in RF tags. To accommodate this need, in a manner that scales with with the number of nodes, the number of distinct paging signals has to be much less than the number of possible nodes. This is accomplished through a group based wake up scheme, that initially awakens the targeted node along with a number of other similarly disposed nodes that subsequently return to their original sleep state. Trade-offs among energy consumption, delay as well as overhead are presented; comparisons with other protocols show the potential for 16 to 50% improvement in energy consumption.