Low-Cost IoT Smart-Home Node for Motion and Gas Leakage Monitoring with Arduino and ESP8266

This paper presents the design and validation of an affordable, retrofit-friendly smart-home platform that couples assistive automation with early hazard detection. The architecture integrates an Arduino-class microcontroller for deterministic, time-critical I/O with an ESP8266/NodeMCU network front-end that exposes a lightweight, browser- or app-based interface. Two complementary sensing streams drive the control policy: a passive infrared (PIR) sensor for occupancy-aware actuation of lighting and ventilation, and an MQ-2 module for detecting liquefied petroleum gas, methane, hydrogen, and smoke. All mains loads are switched through opto-isolated relays, and safety logic executes locally to avoid dependency on cloud availability. A single state machine prioritises safety over convenience, implements on/off hysteresis and minimum-run timers to prevent relay chattering, and publishes events to the handset in real time. A bench-scale prototype demonstrates reliable manual overrides, motion-triggered automation without nuisance toggling after calibration, and prompt phone notifications during staged smoke/gas events. Normalising the gas sensor response to its clean-air baseline and combining PIR hold-time with software debouncing proved essential to stability. The minimal bill of materials and widely supported toolchain lowers the barrier to replication and extension. We conclude that meaningful gains in day-to-day convenience, prospective energy savings, and time-to-awareness for domestic hazards can be achieved with inexpensive components when paired with a disciplined, locally deterministic control strategy.