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Youth screen media activity is a growing concern, though few studies include objective usage data. Through the longitudinal, US-based Adolescent Brain Cognitive Development (ABCD) Study, youth (mage= 14; n= 1,415) self-reported their typical smartphone use and passively recorded three weeks of smartphone use via the ABCD-specific Effortless Assessment Research System (EARS) application. Here we describe and validate passively-sensed smartphone keyboard and app use measures, provide code to harmonize measures across operating systems, and describe trends in adolescent smartphone use. Keyboard and app-use measures were reliable and positively correlated with one another (r= 0.33) and with self-reported use (rs= 0.21-0.35). Participants recorded a mean of 5hrs of daily smartphone use, two more hours than they reported, with females using more than males. Smartphone use was recorded at all hours, peaking from 8-10PM and lowest from 3-5AM. Social media and texting apps comprised nearly half of all use. Data are openly available to approved investigators (https://nda. nih. gov/abcd/). Information herein can inform use of the ABCD dataset to longitudinally study health and neurodevelopmental correlates of adolescent smartphone use.