Self-administered Neurostimulation Intervention for Firefighter Traumatic Stress to Reduce Alcohol Use: Pilot Study

The goal of this clinical trial is to evaluate the feasibility, acceptability, and appropriateness of a transcutaneous auricular neurostimulation (tAN) protocol in firefighters who engage in heavy drinking, have at least a mild alcohol use disorder, and report above-average posttraumatic stress symptoms (PTS). The main questions it aims to answer are: * How feasible do firefighter participants rate the study procedures on the Feasibility of Intervention Measure? * How do firefighter participants rate the acceptability of the study procedures (Acceptability of Intervention Measure) and the appropriateness of the tAN device (Intervention Appropriateness Measure)? Researchers will compare an active tAN condition (receiving therapeutic stimulation from the Sparrow device) to an active sham condition (receiving stimulation below a therapeutic level) to see if the intervention reduces PTS symptom severity and heavy drinking events, and to evaluate the clinical effects on insomnia, mental health symptoms, and quality of life. Participants will: * Use the Sparrow device for at least 1 hour/day for 5 days/week throughout a 4-week treatment phase. * Complete daily measures of traumatic event exposure, PTS symptom severity, alcohol use, and trauma-related drinking motivations. * Complete audio journals capturing their experience with symptoms and the device. * Wear sensors to record heart rate, heart rate variability, and sleep data throughout the intervention phase. Complete assessments immediately following treatment (Week 4) and one month later (Week 8).