This review article discusses various techniques of environmental monitoring (EM) systems and what is required for the variations in hardware implementation and/or algorithmic logic. This review presents an overview of the existing state-of-the-art practices of environmental monitoring systems and is mainly focused on energy-efficient and low-cost environment monitoring systems. The following are some of the major factors that usually rule the development of EM systems, namely, energy efficiency, cost of the overall system, response time of the sensor module, good accuracy of the system, adequate signal-to-noise ratio, radio frequency interference/electromagnetic interference (RFI/EMI) rejection during varying atmospheric conditions and in inhomogeneous environments, a user friendly interface with the computer, and complexity of computation. The above concerns are also recognized by reference to research articles on environmental monitoring systems. Emphasis is on the necessity of robust systems that address all or most of the above mentioned criteria.