: In this paper, we present a two-tiered scheduling approach for effective energy conservation in wireless sensor networks. The effectiveness of this mechanism relies on dynamically updated two-tiered scheduling architecture. We aim to prolong network lifetime, while preserving the major requirements of wireless sensor networks: coverage and connectivity. In this approach, sensors are periodically scheduled into sleep in two phases using weighted greedy algorithms that can be deployed either centralised or distributed. First, we establish a coverage-tier by selecting a set of sensors that fully covers the sensing field. Thus, sensors that are not selected for the coverage-tier, are put into sleep immediately. However, the coverage-tier sensors do not necessarily stay active all the time when events are not reported. Therefore, a second tier, called connectivity-tier, is formed to deliver data traffic to a sink node. Thus sensors, essential to coverage-tier but not in connectivity-tier ...