This study presents the development and validation of a unique Digital Experience Sampling Method (ESM) questionnaire specifically adapted for monitoring changes in the mental state of patients during psychiatric hospitalization. The questionnaire was carefully crafted through focus groups involving patients and clinical staff, ensuring its relevance and applicability to the unique characteristics of mental state changes in a hospitalization setting. To evaluate the validity of the ESM questionnaire, symptom severity trends obtained from the questionnaire will be compared with estimates derived from the Positive and Negative Syndrome Scale (PANSS) assessment. Data will be collected from 100 subjects over a 14-day psychiatric hospitalization period. In addition to the ESM questionnaire, smartwatch sensors will monitor physiological indicators. Feasibility and patient compliance will be assessed by examining patients' willingness to use the digital ESM questionnaires and the smartwatch sensors. The study will also cross-reference self-reported sleep quality and activity levels captured in the ESM questionnaires with objective physiological indicators and nursing staff reports, providing insights into the reliability of the patient-reported data. Furthermore, the study will evaluate the impact of the ESM data on clinical decision-making by physicians throughout the 14-day psychiatric hospitalization period. Patient satisfaction and satisfaction among the multidisciplinary team with the monitoring model will also be assessed. This research underscores the potential of digital technologies to enhance patient-centered care and facilitate informed treatment decisions in psychiatric hospitalization settings.