## 1 Introduction
### Aims and Contributions of the Presented Research Work  
The following scientific work presents the development of a smart garment designed for monitoring biophysical and environmental parameters. The wearable device consists of a sweatshirt equipped with multiple sensors, namely, a photoplethysmography (PPG) sensor to monitor heart rate (HR) and SpO\({}_{2}\), temperature sensors to acquire body and air temperatures, an integrated accelerometer to detect falls and step count, and custom electrochemical gas sensing modules to measure the concentrations of dangerous gas species (CO, H\({}_{2}\)S, and CH\({}_{2}\)O), as well as the oxygen level (O\({}_{2}\)). Among the various gas sensor types, electrochemical gas sensors were chosen for the wearable application. The advantages of electrochemical gas sensors include reduced power consumption and size, making them ideal for wearable devices [31; 32; 33]. Unlike semiconductor gas sensors, electrochemical ones do not need to bring the sensitive material, specifically the semiconductor, to the working temperature (of the order of 100-400 \({}^{\circ}\)C) through a resistor, resulting in greater current consumption that would affect the energy performance of the wearable application. Compared to optical sensors, the advantages of electrochemical gas sensors include their lower costs and smaller sizes, simplifying their integration. However, the typical drawbacks of electrochemical sensors are their high sensitivity to external agents such as temperature and humidity, cross-sensitivity (i.e., interference due to the presence of other gases to which the electrodes are sensitive), and rather short life span (around two years on average) [34]. Among the gas species monitored by the wearable device, carbon monoxide constitutes an insidious danger because it is odorless, colorless, and toxic [35]. This gas species is emitted by combustion processes lacking oxygen, as happens in stoves, boilers, and furnaces. Because its usage or emission is connected to various production activities, it can be found in various industrial settings (food, chemical, metallurgical industries, etc.). Additionally, H\({}_{2}\)S is commonly used in diverse industrial activities, from the food preservation industry (e.g., sugar bleaching and conservation of wine and meat) to the purification of thermal waters and oil refining. Long exposure to its fumes can cause extensive damage to various body systems: it can paralyze the olfactory nerve, making it impossible to perceive, and can cause unconsciousness within a few minutes. Exposure to low concentrations in the air can irritate the eyes and throat and, in the long term, cause fatigue, confusion, and memory problems. Furthermore, CH\({}_{2}\)O is a colorless gas with a pungent odor that is highly soluble in water [36]. The International Agency for Research on Cancer (IARC) highlights that this compound is carcinogenic to humans and, in particular, causes cancer of the nasopharynx (nasopharynx) and leukemia. Exposure to formaldehyde has also been positively associated with sinus cancer. Exhaust gases from vehicles, power plants, incinerators, and stoves, as well as cigarette smoke, are the main sources of exposure for the general population. In the workplace, on the other hand, all those who work in industries involving adhesive or insulating plastic products or where there is extensive use of paints for woodworking, as well as in the food industry, are exposed to much higher and potentially more dangerous concentrations. Finally, O2 monitoring can be extremely useful for people, such as miners, who operate in enclosed spaces, where the air may become unbreathable due to poor air exchange. Additionally, a device using an O2 sensor could be useful for users who, either for recreation or work, operate at high altitudes where the air is so thin that it could cause discomfort or fainting. Table 1 summarizes the main limits of the aforementioned gas species according to international or European regulations.