Cranial Electrotherapy Stimulation: Piloting a Road to PTSD Prevention in First Responders

The goal of this study is to test whether active duty firefighters find it possible and suitable to do cranial electrotherapy stimulation (CES) at home, and test whether CES influences measures of depression and posttraumatic stress. The main questions it aims to answer are: * is CES feasible and acceptable in a population of firefighters, and * does CES changes symptoms of posttraumatic stress and depression as well as feelings of anxiety, and fatigue in firefighters. Participants will * complete four weeks of CES at home, and * complete daily assessments of affect and fatigue, and * complete self-reported symptoms of depression and posttraumatic stress before and after four weeks of CES at home Participants maybe asked to * complete an MRI scan before and after four weeks of CES at, and * wear a device to measure their heart rate and sleep quality.