A novel self-organizing sub-network (SOS) protocol that improves the lifetime, scalability, and reduces the overall energy consumption is proposed for wireless sensor networks (WSN). In SOS protocol, the nodes are usually in idle or sleep mode but when an event is detected; the nodes near the event become active and form sub-networks. Subsequently, cluster heads (CHs) are selected within each sub-network, and the nodes are grouped into clusters. Nodes in the cluster send data to their respective CH, which in turn aggregates the data. This method of forming sub-networks reduces the amount of energy used, because only a part of the network closer to the unexpected event is active, when compared to the other existing methods. The results of SOS protocol obtained using GloMoSim demonstrate that the protocol minimizes the energy consumed, lowers the end-to-end delay, increases the lifetime of the network, and ensures scalability when compared to LEACH protocol. The applicability of SOS protocols for structural heath monitoring is investigated.