Objectives To investigate whether and how PA tracker application use supports PA behavior among older adults during the first 24 months of use. Methods: The changes in PA levels (i.e., time spent in different PA intensities) and between PA categories (i.e., low, moderate, or high based on total PA) were examined between three different time points: before taking the application into use (t0), after 12 months of use (t1), and after 24 months of use (t2). The data was collected by using the International Physical Activity Questionnaire modified for the elderly (IPAQ-E). Results: A statistically significant increase was observed in walking (χ2 (2) = 29.741, p < .001), moderate PA (χ2 (2) = 6.327, p = .042), and total PA levels (χ2 (2) = 11.489, p = .003). The increase was observed between t0 and t1 as well as between t0 and t2. The overall changes between PA categories were statistically significant between t0 and t1 (χ2 (3) = 15.789, p = .001) as well as between t0 and t2 (χ2 (3) = 14.745, p = .002). There were more increasingly active (moved to a higher PA category) than decreasingly active (moved to a lower PA category) participants. Discussion: Overall, the results indicate that PA tracker application use can promote PA behavior among older adults. Stakeholders that work with PA programs and PA promotion, as well as individual users, can utilize digital wellness technologies in supporting PA promotion, especially in exceptional times, like the COVID-19 pandemic, when health care restrictions prevent general gatherings.