## Literature Review  
### IoT-Based Sensor for Monitoring System  
Recent technologies such as IoT, sensors, big data, and machine learning can be utilized for monitoring and can play important roles in predicting disease, improving production, reducing cost, providing an early warning system, and facilitating better decision making for management. Several studies have been conducted on IoT-based monitoring systems and showed significant advantages. [PERSON] et al. proposed an IoT-based framework for monitoring human vital signs [7]. A case study on monitoring footballers' heart rates during a football match was conducted. The proposed system was able to monitor the players' vital signs and predict, not only the worst situation (i.e., sudden death), but also possible injuries. [PERSON] et al. proposed a monitoring system based on IoT for the agricultural field [8]. The developed system was used to monitor citrus soil moisture and nutrients for fertilization and irrigation decision making. Case study-based results showed that the proposed system helped farmers make better decisions, improve citrus production, and reduce labor costs as well as the pollution caused by chemical fertilizers. [PERSON] et al. proposed a distributed monitoring system for leakage detection and gas levels in hazardous environments [9]. A wireless sensor network was utilized to gather the sensor data. The collected environmental sensor data were transmitted to a remote server and presented to the manager via a user interface. The proposed system was effective for monitoring the environment and triggered a warning when critical events were detected. Finally, [PERSON] et al. proposed real-time monitoring based on information modeling and a wireless sensor network to monitor the safety of construction sites [10]. Hazardous gas levels and environmental conditions (i.e., temperature and humidity) were collected by wireless sensor nodes and sent to a remote server. The proposed system triggered a warning/alarm once an abnormal situation was detected. Case-study based results showed that the proposed system improved the safety of the construction site and helped the management with better decision making in real-time. Current studies utilize IoT-based sensors to determine the environmental conditions at a real site, thus the sensor data can be presented in real-time. IoT-based sensors provide an important solution for many research areas, including smart building and healthcare. Several studies have been conducted and showed significant results for IoT based sensors on improving system performance. [PERSON] et al. proposed a monitoring system using IoT-based sensors for smart buildings [55]. The proposed system was implemented in a simulation environment. The results showed that a better monitoring system in a smart building can be achieved by using several IoT-based sensors. The proposed system is expected to improve energy efficiency as well as facilitate green smart buildings. [PERSON] et al. proposed an IoT-based sensor for monitoring the radon gas level inside a building [56]. The proposed system could notify/warn users when a specific level of radon gas is reached to prevent dangerous situations. The proposed system was able to monitor the radon gas level, trigger the programmed actions, and notify the users once a specific level of gas radon was reached. [PERSON] et al. proposed a modular indoor air quality monitoring system that collects several types of sensor data such as CO\({}_{2}\), CO, SO\({}_{2}\), NO\({}_{2}\), O\({}_{3}\), Cl\({}_{2}\), temperature, and humidity [57]. A single-board computer (Raspberry Pi) was utilized as a gateway to process the sensor data. The experimental results showed that the proposed system effectively monitored the indoor air quality for six kinds of gases in addition to temperature and humidity. [PERSON] and [PERSON] proposed a healthcare system based on wearable IoT-based sensors for detecting and preventing the outbreak of chikungunya virus [58].