This document is an M.Tech project report submitted by Divya Prabha to the Department of Computer Science and Engineering at Shaheed Bhagat Singh State Technical Campus in Ferozepur, India in partial fulfillment of the requirements for a Master of Technology degree. The project investigates energy efficient routing protocols in wireless sensor networks. It develops and analyzes the low-energy adaptive clustering hierarchy protocol and proposes a modified version called MODLEACH that introduces an efficient cluster head replacement scheme and dual transmitting power levels. A performance analysis of LEACH and MODLEACH is presented considering metrics like throughput, network lifetime, and cluster head replacements.