Electronic screens (e.g., TV, computers, tablets, smartphones) are now ubiquitous in the lives of children. Research suggests that electronic screen use may offer both benefits (e.g., early learning, social contact and support) and risks (e.g., low physical activity/fitness, poor sleep quality, obesity) to the overall well-being of children (1-10). However, the ability to assess the relationship of screen exposure to behavioral and health outcomes is plagued by multiple measurement issues (11,12). To date, studies of electronic screen use in children have relied largely on parental or caregiver self-report, which is susceptible to high levels of error and is limited in its ability to capture the short bouts of screen use that are characteristic of newer media (e.g., smartphones) (13-21). Some groups have developed smartphone apps or TV/computer allowance devices that measure screen usage more objectively (22-24), but these systems often require instrumenting every screen in a person's environment, thus severely limiting real-world application and generalizability. A more precise, scalable, and cost-effective measure of screen use is needed to understand and evaluate screen time effects on child behaviors and health outcomes.