In this paper we introduce the Worktivity mobile app as a potential solution to help reduce occupational sitting in an office environment. Worktivity functions by sending hourly reminders to stand up or move in addition to showing factual information related to the benefits of being active within the office environment. The Worktivity app was used over a period of 8 weeks by 37 participants aged between 18 and 65 years old from two private office worksites in Northern Ireland. Results demonstrated how users responded to the reminders over the duration of the study with mean acknowledgement rates of 66.06% and 51.57% when using the app and when using the app with a standing desk, respectively.