Wireless Sensor Network (WSN) is a system used to conduct a remote monitoring in a wide monitoring area. It has a sensor node - a sampling point - which communicate each other to passing their data to central node for recapitulation or transmit it to data center. Because of that, communication system is a crucial thing for WSN. However, WSN may be deployed in a environment that far from ideal condition. Placed in an unattended area with far distance between nodes, WSN is very vulnerable with security threats. To overcome that, the good combination between communication protocol and encryption algorithm for WSN is needed to gather an accurate and representative data with high transmission speed. This research focused on finding those combination for our own-made low-cost sensor node for CO2 monitoring. In this research, two routing protocols (AODV and TARP) and several encryption algorithms (AES, ChaCha, and Speck) tested to determine which combination is give the best result. As the result, combination between routing protocol AODV and encryption algorithm Speck give the best result in the term of performance.