Non-communicable diseases impose a global burden, with physical inactivity as a key modifiable risk factor. Digital interventions can initiate behavior change, yet sustaining these changes is challenging. This pilot study evaluates two reminder strategies—Just-in-Time (JIT) and fading reminders—in fostering habit formation among 18 participants randomized into four groups (JIT, two fading conditions, and a control) using a mobile app to track morning exercise routines. Results reveal that JIT reminders significantly boost initial habit adoption, while fading reminders promote greater habit strength. A structured, gradual transition between reminder types appears critical for long-term habit maintenance and automaticity. Furthermore, this study contributes a research model that integrates reminder strategies, habit strength, and behavioral outcomes, offering a theoretical framework for designing tailored digital interventions to reinforce lasting behavioral change as part of digitally transformed, patient-centered healthcare.