["Journal of Research on Adolescence, Volume 36, Issue 2, June 2026. ", "\nAbstract\nAdolescents are among the most frequent smartphone users worldwide. Yet, few studies have examined how smartphone use appears among minority adolescents, including sexual and gender minority (SGM) youth and children of immigrant parents, who often experience unique stressors and heightened mental‐health risk. Passive smartphone monitoring provides a promising, low‐burden method for continuously and objectively assessing real‐world behavior, offering new opportunities to identify dynamic markers of mental health challenges, including suicide risk, in daily life. The present study evaluated the feasibility of a replicable framework for passive smartphone monitoring among adolescents at high risk for suicidal thoughts and behaviors (STB) and explored longitudinal differences in smartphone‐derived behavioral features across minority subgroups. Ninety‐nine adolescents aged 11–18 with recent STB completed baseline assessments and installed the iFeel app, which collected passive smartphone data for 6 months, including total and social‐media screen time and phone‐inactivity‐based proxy sleep indicators inferred from nighttime phone inactivity. Participants contributed 1500 participant‐weeks of data, with an average of 11.9 weeks of valid monitoring, supporting the feasibility and acceptability of this approach. Daily smartphone use time, social‐media activity time, and sleep duration were comparable to normative adolescent data. No significant longitudinal differences emerged between SGM and non‐SGM adolescents. However, immigrant‐origin adolescents displayed shorter but more stable sleep patterns compared to non‐immigrant origins, who exhibited longer baseline sleep with steeper declines over time. Findings highlight passive sensing as a feasible, inclusive, and scalable method for examining real‐world behavioral processes associated with STB and mental health outcomes among diverse adolescents. This framework offers a scalable approach that future studies can apply to deepen real‐time understanding of mental‐health challenges and behavioral patterns among diverse adolescents.\n"]