Objective: To assess the usability and acceptance of activity tracking technologies by older adults. Method: First in our multimethod approach, we conducted heuristic evaluations of two activity trackers that revealed potential usability barriers to acceptance. Next, questionnaires and interviews were administered to 16 older adults (M_age = 70, SD_age = 3.09, range_age = 65-75) before and after a 28-day field study to understand facilitators and additional barriers to acceptance. These measurements were supplemented with diary and usage data and assessed whether and why users overcame usability issues. Results: The heuristic evaluation revealed usability barriers in System Status Visibility, Error Prevention, and Consistency and Standards. The field study revealed additional barriers (e.g., accuracy, format) and acceptance-facilitators (e.g., goal tracking, usefulness, encouragement). Discussion: The acceptance of wellness management technologies, such as activity trackers, may be increased by addressing acceptance-barriers during deployment (e.g., providing tutorials on features that were challenging, communicating usefulness).