Wireless Sensor Networks (WSNs) consist of numerous sensors which send sensed data to base station. Energy conservation is an important issue for sensor nodes as they have limited power. Many routing protocols have been proposed earlier for energy efficiency of both homogeneous and heterogeneous environments. The authors can prolong their stability and network lifetime by reducing their energy consumption. In this paper, they propose a protocol designed for the characteristics of reactive homogeneous WSNs, HEER (Hybrid Energy Efficient Reactive) protocol. In HEER, Cluster Head (CH) selection is based on the ratio of residual energy of node and average energy of network. Moreover, to conserve more energy, they introduce Hard Threshold (HT) and Soft Threshold (ST).