Many ordinary behaviors in daily life can have an extraordinary impact on health. These ordinary behaviors, such as physical activity or fluid intake, become second nature and automatic for some. Others struggle with these behaviors, especially when their lives are busy and competing goals vie for their attention and effort. One solution for this sizable latter group involves using just-in-time adaptive interventions to tailor intervention delivery to moments of opportunity or vulnerability. In this talk, I will describe ongoing work that leverages technology to monitor contextual changes and inform micro-intervention decisions in two digital messaging interventions. The first example involves a physical activity intervention that applies tools from control systems engineering to develop person-specific models of physical activity dynamics and decision rules based on those models. Inputs in these models include a person’s recent physical activity, the day of the week, momentary location-specific weather conditions, and historical responses to different message content (e.g., move more, sit less). Those person-specific models are used to determine if a message at that moment would be expected to increase physical activity and which message would be best to send. The second example involves a fluid intake intervention for patients with kidney stones. It integrates a connected water bottle, mobile application, and a custom smartwatch app that detects drinking gestures into a semi-automated tracking system to detect drinking behavior. When patients with goals to drink regularly throughout the day lapse, the system delivers delightful reminders to drink via multimedia text messages. These digital tools illustrate the potential for drawing on contextual information to deliver interventions at moments of opportunity or vulnerability. They represent one step toward realizing a vision of precision behavioral interventions for physical activity and behavioral nutrition.