Various efforts have been made to automate irrigation systems, however, there still exists a problem of an impending water crisis that was reported by the World Bank wherein the Philippines was one of the countries that will be affected. Most irrigation systems that were designed for open field farms require a lot of meteorological data that can only be acquired from weather stations, which are not readily available to some places. For these reasons, the researchers developed an evapotranspiration (ET)-based sensing irrigation system where less meteorological data are required to estimate the ET of a Capsicum frutescens plant (siling labuyo). This study covers the development of an automatic irrigation system with control based on the ET of the C. frutescens plant, which is also computed by the system software using sensor readings of temperature and water flow. The system was also able to implement a deficit irrigation strategy. The results have shown that the proposed system used up to 20% less water than the ET-based irrigation systems designed to use 100% crop ET, without any significant decrease in crop yield.