Poor indoor environmental quality (IEQ) has become a global concern for World Health Organization (WHO), and its impact on health and well-being has been exacerbated by the COVID-19 pandemic. To monitor and sanitize indoor air, this study develops a cost-effective and customizable IEQ monitoring system to detect unhealthy and low-comfort air levels. This system uses ThingSpeak (MATLAB), microcontrollers (Arduino Uno), and various low-cost sensors to measure indoor air quality (IAQ) and IEQ in terms of gas, particulate matter, temperature, sound level, and ultraviolet (UV) light. The presented system is validated with respect to temperature, relative humidity, and particulate matter by benchmarking against the Camfil air image sensor manufac...