Liquefied petroleum gas (LPG) is a common household and commercial fuel, but undetected leaks and unexpected cylinder depletion create serious safety and convenience risks. Internet of Things (IoT) technology is increasingly proposed to monitor cylinders continuously, warn users and, in some designs, act automatically. This paper pre-sents a focused narrative review of five peer-reviewed studies published between 2021 and 2024 in Elsevier, MDPI, IEEE, Springer and Balkan Journal of Electrical and Computer Engineering venues that propose smart LPG cyl-inder safety systems. The review compares sensing (MQ-series gas sensors, load cells, temperature sensors), con-trol and communication (Arduino-class and Wi-Fi microcontrollers, cloud platforms, SMS and app alerts) and pro-tective action (buzzers, exhaust fans, regulator or valve shut-off, automatic refill booking). The reviewed systems share a common architecture of gas sensor, load cell, microcontroller and cloud alerting, and differ mainly in the actions they trigger and the analytics they add. Reported evidence is mostly prototype-level: quantitative accuracy, response time, sensor drift, long-term field operation, connectivity failure and cybersecurity are rarely reported. The paper contributes a comparative table, a gap analysis and a set of research directions for reliable, fail-safe smart cylinder systems.