## 1 Introduction
The use of a motherboard allows the connection of peripherals that help in capturing information on physical and chemical parameters of IAQ. Specifically, between 67% and 70% of the sensors that monitor IAQ are intended to measure CO\({}_{2}\)[78; 79]. Measurement range, sensitivity, and response time are their key sensors features. In addition to the two elements described, a communication unit must be included. This enables data storage, processing, and further analysis to be performed [79]. The interconnection of clonic devices with other systems favors the use of the Internet of Things (IoT) and data storage in the cloud. These enabling technologies allow wirelessly collected data to be evaluated for interpretation, in real time or deferred, for a real monitoring and control of the IAQ [79; 80]. This has the potential to transform an existing building to be renovated into a smart building [81]. Several researches have studied the application of IoT for IAQ control [82; 83]. They stress the advantages of system integration with connections to smartphone applications, ease of installation and scalability as an element to achieve cost improvements [84]. In this regard, [PERSON] et al. [85] developed research on an IoT solution that monitors CO\({}_{2}\) concentration in smart buildings. In this way, the IAQ can be controlled and therefore, the health of the occupants be improved. It can be noted that clonic devices present a series of limitations. These are related to the maintenance and calibration of the sensors assembled, the communication protocols, and their power consumption [86]. Fortunately, with the aim of creating devices that help to promote healthy, sustainable, and smart cities, considerable progress has been made in recent years dealing with these issues [79]. The first objective of this research was to design, develop, assemble, and prototype a low-cost clonic device to provide buildings [87] with smart functionalities in the IAQ field [88]. As indoor comfort is currently taking a back seat to the priority of maintaining safe CO\({}_{2}\) levels to protect from COVID-19, research focused on the use of CO\({}_{2}\) sensors. Another purpose addressed was the choice of the best location to place the clonic device. To this end, computational fluid dynamics (CFD) simulations [89] were carried out in different scenarios (ventilation options) for a living space that was used as case study. It can be noted that, to the best of our knowledge, this has not been addressed before. Once the best locations for the placement and distribution of the instruments were determined, an experimental study was performed. Data were obtained with a calibrated equipment that was used as a reference standard and also with the low-cost prototype device. Comparisons were then made to check if measurements were acceptable for IAQ monitoring and control. In summary, the three main objectives and their relationship are shown in Figure 1:  
* CFD analysis of the interior air flows of a living space to establish the location of measurement points. * Exhaustive analysis of the solution to design and develop the prototype. * Calibration of the cloning device for proper data acquisition. The main novel contributions of this paper can be summarised in the following four elements:  
* Complete design, development, and prototyping of a clonic device for CO\({}_{2}\) measurement as a control and monitoring parameter for IAQ. This parameter relates to air renewals for minimizing the spread of COVID. We showed all the physical components (sensor, microprocessor board and connections) and the programming code necessary for its operation. * Description in detail the calibration protocol. In this paper, we used the KIMO HQ-210 commercial instrument as a reference standard for the clonic device. However, other instruments of similar characteristics with a calibration certificate from a laboratory legally accredited for this purpose could have been selected.