## 2 Materials and Methods
### Data Recording and Analysis  
The experiment involved 37 healthy individuals, aged 20 to 30 years, including 20 men and 17 women, all of whom provided informed consent. Participants were fully briefed on the research objectives and procedures and consented to the processing of personal data for scientific experiments. The study adhered to the ethical standards outlined in the Declaration of Helsinki (1975, revised in 2000), complied with relevant national laws [32], and was approved by the Ethics Committee of Kharkiv National Medical University (Protocol No. 01-13/12 dated 12 October 2024). Moreover, all data records were anonymized. Inclusion Criteria:  
1. Healthy individuals aged 20-30 years;
2. Participants capable of providing informed consent;
3. Individuals with no history of cardiovascular or endocrine diseases, ensuring a homogeneous baseline for stress-response evaluation;
4. People who had never previously experienced air raid sirens participated in the study. All of them are currently residing in Germany, having arrived there before the war began. Exclusion Criteria:  
1. Participants with chronic stress conditions or psychological disorders. 2. Individuals with hearing impairments that could affect their perception of the air raid siren. 3. Those with previous traumatic experiences related to sirens (to minimize confounding psychological responses). Training and Test Dataset Sizes: To ensure a robust evaluation, it was verified that the records in the test dataset were different from the records in the training dataset. This separation ensures that the model is evaluated on unseen data, which reflects its ability to generalize. The experiment included acquisition of PPG and GSR data under both stress-free conditions and in the presence of stressors. The hypothesis was to identify correlations between participants' physiological states, with prior knowledge of the stressor's presence and its duration. Figure 1 illustrates the experimental setup. Figure 1 shows the placement of the PPG and GSR sensors, which are in the Shimmer device, attached to the participant's hand, placed on two fingers of one hand, as well as the PPG sensor placed on the earlobe. All signals were recorded simultaneously, at a sampling frequency of 128 Hz and exported to.csv format. The data are collected and transmitted in real time via Bluetooth to a personal computer using the Consensys PRO software [31], which enables data storage and processing, including the calculation of HRV data from inter beat intervals (IBI). The experimental protocol is outlined in Figure 2. The total measurement took 14 min and consisted of a resting phase (5 min) as an acclimation period, measurement without stressors (3 min), measurement during an air arid signal (3 min), and a recovery phase (3 min). Each session started with a 5 min resting phase to establish a baseline, followed by a 3 min data collection phase to perform measurement without stress, then a 3 min measurement while listening to an air arid siren, and finally a 3 min recovery period to return to baseline. During the experiment, participants were positioned in front of a white screen to minimize any additional emotional stimuli and ensure consistent conditions across all trials. This setup allowed participants to focus without being distracted by changes in visual content, while the stress-inducing stimulus was delivered through headphones. Due to human factors, the duration of measurements may vary slightly, as the start and end of signal recordings were initiated manually. To mitigate errors, measurements were conducted for 10 s longer than the required duration. Data recorded beyond the protocol duration were then automatically removed for all recordings, ensuring that the results were standardized to a uniform duration. The air arid siren was selected as the stress-inducing stimulus due to its relevance to the current situation in Ukraine, where most of the members of our research group come from.