The Development and Protocol for Testing a Co-Created Digital Intervention (Sentinel) to Improve Mental Well-Being and Help Manage and Prevent Trauma in First Responders.

First responders face significant mental health risks from occupational trauma exposure including acute stress, PTSD, burnout, and other adverse mental health outcomes.

• First responders and frontline workers are frequently exposed to traumatic events within their professional roles
• There remains a lack of evidence-based digital interventions tailored to meet their unique mental health needs
• Participants were drawn from fire services, police, and emergency health sectors

Phase 1 of the Sentinel development involved in-depth qualitative interviews with 54 first responders to explore mental health needs, barriers to accessing support, and views on digital interventions.

• 54 FRs were interviewed from fire services, police, and emergency health sectors
• The interviews explored mental health needs, barriers to accessing support, and views on the potential role of digital interventions
• Findings from phase 1 were integrated with existing evidence, policies, and theoretical frameworks in phase 2 to develop intervention content

The Sentinel development followed a rigorous 4-phase approach including market analysis, content development, prototype testing, and a feasibility study.

• Phase 1 consisted of market analysis and qualitative interviews
• Phase 2 involved developing content by integrating phase 1 findings with existing evidence, policies, and theoretical frameworks
• Phase 3 involved testing a high-fidelity clickable prototype through co-design workshops, iterative development sprints, and usability evaluations
• Phase 4 is a mixed methods, nonrandomized feasibility study to evaluate acceptability, usability, safety, and implementation potential

The Phase 4 feasibility study is designed to collect quantitative data from up to 100 first responders and qualitative data from 30 FR participants and 20 health and social care professionals.

• Quantitative data will be collected from up to 100 FRs
• Qualitative interviews will be conducted with 30 FR participants
• 20 health and social care professionals who refer FRs to the intervention will also be interviewed
• The study evaluates Sentinel's acceptability, usability, safety, and implementation potential

As of January 16, 2026, pilot testing had recruited 119 participants who completed the initial survey, with 59 having downloaded the Sentinel app.

• Pilot testing began in August 2025 and is planned for completion by August 2026
• 119 participants completed the initial survey as of January 16, 2026
• 59 participants had downloaded the Sentinel app
• 24 participants had used the app for 6 weeks and completed the follow-up survey
• 13 participants had consented to an interview

The co-creation process was identified as essential in ensuring Sentinel meets the specific needs of first responders and frontline workers.

• Preliminary feedback highlights the app's relevance and usability
• Feedback from FRs and frontline workers during phase 3 was used to refine the app's design and functionality
• The intervention content reflected the lived experiences of FRs by integrating qualitative findings with existing evidence

The authors report being on track to meet target recruitment sample, with data intended to inform refinements and determine readiness for a larger efficacy trial.

• Recruitment is described as on track as of January 16, 2026
• Data will provide detailed insights to inform refinements
• The feasibility data will determine readiness for a larger efficacy trial
• Future work will evaluate Sentinel's capacity to improve mental well-being, support trauma recovery, and build resilience