We expect that participants will be in this research study for six months. Participants will be asked to download an app on their smartphone. This app will collect data from the phone's sensors. Participants will also be asked to answer some questions about their mood each month.

This study is randomized which means that in order to learn about the effect of the Smartphone App, half the people in this study will use it, and the other half will not. If participants decide to enroll into this research study, they may be assigned by chance to download a Smartphone App. This App will collect data from the phone's sensors. Participants will also be asked to complete questionnaires about their mood each month.

This study is randomized which means that in order to learn about the effect of the Smartphone App, half the people in this study will use it, and the other half will not. If participants decide to enroll into this research study, they may be assigned by chance to have usual care. Participants will be asked to complete questionnaires about their mood each month.

The Mood Triggers application, developed by Dr. Jacobson, will be used for collecting smartphone sensor data. This HIPAA-compliant app has been incorporated into various projects at Dartmouth, Stanford, and MGH/Harvard, with development supported by NIDA, NIMHD, NCI, and the Department of Veterans Affairs. The Mood Triggers app will capture a wide range of metrics, including psychomotor agitation, sleep disturbances, low behavioral activation, social contact, exposure to natural light, heart rate, heart rate variability, and screen time. The app also tracks the patient's screen time and app usage data. The Mood Triggers App will be installed on the smartphones at time of informed consent for all 120 patients enrolled in Phase 1 and for 100 clinical trial participants randomized to the "early warning system" (intervention arm) in Phase 2. Data will be collected from the Mood Triggers App starting on day of discharge from care and for 6 months post-discharge date.

The 9-item Patient Health Questionnaire (PHQ-9), a validated self-reported depression questionnaire, will be used to detect monthly depression recurrence based on past-month MoodTriggers application data. The PHQ-9 scores range from 0-27, with higher scores reflecting higher depression symptom levels. The PHQ-9 will be used to detect monthly recurrence of Major Depressive Disorder (MDD; PHQ-9 scores ≥ 10) during Phase 1 in all 120 participants. For the randomized clinical trial in Phase 2, we will capture the PHQ-9 monthly in both arms (MoodTriggers app vs. no app) for 6-months following discharge.

A subgroup of individuals from Phase 1 will be invited and verbally consented to participate in semi-structured interviews to provide their experiences with the study's digital biomarker "early warning" system. The purpose of this interview is to identify perceived benefits and barriers of depression monitoring using passive sensing data collection from your mobile phone. The information gathered will be used to evaluate the effectiveness of the Mood Trigger app in predicting symptoms of depression.