Hexanal detection is essential for real-time monitoring of oil oxidation stability and evaluating health impact. Nevertheless, accurately monitoring hexanal levels in the presence of other volatile organic compounds (VOCs) remains a significant challenge. In this article, we present an In2O3/SnO2 composite-based electrochemical gas sensor that offers excellent selectivity for hexanal over other tested VOCs, such as styrene, acetone, and n-hexane, and featured a remarkably low detection limit of approximately 50 parts per billion (ppb). In addition, a gas sensing device that integrated the aforementioned electrochemical hexanal sensor with blockchain technology was developed to facilitate remote monitoring of hexanal variations. In particular, shuffling technology and digital signatures were utilized to bolster the security of data transmission and access. It turns out that the developed sensing device demonstrated impressive performance in both sensing accuracy and data security, highlighting its potential as a promising solution for remote hexanal monitoring.