## 5 Discussion  
In this study, we investigated the utility of GSR and PPG data as indicators of stress. While the GSR is widely recognized as one of the most reliable measures of stress, its interpretation is relatively complex compared to PPG. A primary challenge in evaluating GSR results lies in the variability of the GSR under physiological conditions. The GSR is influenced by numerous external factors, such as air temperature and humidity, as well as internal factors, including sweat gland activity and the presence or absence of underlying pathologies. To address this variability, we evaluated changes in the GSR rather than absolute values, comparing measurements taken during stress with those obtained in a resting state. Additionally, by assessing the GSR during the recovery phase, we identified the signal recovery rate, which reflects an individual's ability to adapt to stress. We consider the rate of decrease in resistance--and corresponding increase in conductivity--to be an important indicator for assessing the impact of stress on the body. As a result, four groups were identified depending on the nature of their GSR responses:  
Group 1: Individuals exhibited a rapid decrease in skin resistance right after the siren started, followed by a swift return to baseline once the stressor ended. This pattern suggests a highly adaptable nervous system capable of quickly adjusting to stress, enabling effective decision making and stress management (Figure 8). Group 2: Participants in this group also showed immediate responses to the stressor. The skin resistance signal began to return to its original level later in the second part of the recovery phase, but still did not reach the original pre-siren level. Such a delayed response may indicate a degree of refractoriness in their nervous systems (Figure 9). Figure 8: Skin resistance data for Group 1. Group 3: This group responded quickly to stress in the same way as Group 1 and Group 2 but took longer to recover, with skin resistance nearly returning to baseline in the second half of the recovery phase. In the first part of the recovery phase, the signal almost reached the pre-stress level, but then its amplitude decreased even more significantly, indicating an increase in stress. Prolonged recovery may reflect insufficient adaptability, heightening susceptibility to stress and amplifying its negative effects (Figure 10). Group 4: Individuals in this group also showed a rapid response to stress but recovered slower than Group 1 and slightly faster than Groups 2 and 3. Although faster recovery is advantageous, a significant drop in signal amplitude at the end of the recovery phase indicates a return of stress as at the onset of the si  
Figure 11: Skin resistance data for Group 4. Figure 10: Skin resistance data for Group 3. Figure 9: Skin resistance data for Group 2. To simplify visualization, we have excluded the 5 min resting phase from graphs 8-11, (mark shows the end of 3 min no stress). According to the protocol, each measurement now lasts 9 min (3 min no stress, 3 min stress, 3 min recovery). Thus, we assume that physiologically the most appropriate stress response is a rapid stress response and a rapid return of values to pre-stress levels, which corresponds to Group 1. Since the siren signal refers to a stressor that requires an immediate response, as it poses a direct threat to human life, the physiological response to such a signal should be rapid. Moreover, not only was the change in the skin resistance signal amplitude during the stress response observed, but also the rate of its change immediately after exposure to the stress factor, as well as the rate of change in the signal amplitude during the recovery phase. This opens prospects for future research. In this regard, a new interpretation is given to the study [47], according to which stress can be classified by the degree of increase in conductivity as follows: 1. Mild: increase by 10-20%, 2. Moderate: increase by 21-30%, 3. Severe: increase by 31-50% and more.