Energy-Efficient and Security-Conscious Design of a PIR-Based Motion-Responsive Lighting System: Bridging Occupancy Sensing and IoT Threat Mitigation

Conventional static lighting systems in residential and institutional environments remain a principal driver of unnecessary electrical energy consumption, particularly in contexts characterized by irregular and unpredictable occupancy patterns. Beyond inefficiency, the growing integration of embedded sensing and actuation hardware into building infrastructure introduces a parallel and frequently overlooked concern: such low-cost, often security-naive devices constitute an expanding attack surface within increasingly networked smart-building ecosystems. This study presents the design, hardware implementation, firmware development, and empirical evaluation of a low-cost, occupancy-driven motion-responsive illumination system founded on Passive Infrared (PIR) sensor technology interfaced with an Arduino Uno microcontroller, accompanied by a structured security-aware analysis of the system's architecture and deployment implications. In parallel, the system architecture was subjected to a threat-modeling analysis to identify cybersecurity-relevant weaknesses inherent to its embedded design. The system continuously monitors a designated indoor space and autonomously activates connected lighting loads upon detecting infrared radiation differentials attributable to human motion, subsequently deactivating the load after a configurable inactivity timeout of 12 seconds. Hardware components comprising an HC-SR501 PIR sensor, ATmega328P-based microcontroller, single-channel relay module, and LED illumination element were assembled and tested across multiple indoor scenarios including variable occupancy conditions, ambient illumination levels, and spatial configurations. Empirical evaluation yielded an aggregate detection accuracy of approximately 85%, a mean response time of 0.8 seconds, and an estimated energy reduction of up to 94% relative to manually operated conventional lighting over equivalent operational periods. The system demonstrated consistent and reliable functional performance across all evaluated scenarios, with residual limitations attributable to line-of-sight constraints and the inherent insensitivity of PIR technology to stationary occupants. The findings establish both the technical viability of PIR-microcontroller integration as an affordable, scalable strategy for demand-side lighting energy management in resource-constrained environments, and the necessity of incorporating baseline security safeguards prior to any networked extension of such systems, with particular relevance to Sub-Saharan African contexts characterized by persistent electricity supply deficits and accelerating smart-infrastructure adoption.