An activity monitoring and reminder deliveryframework, referred to as iMessenger, is presented. iMessengerincludes five independent modules and adopts alayered structure to assemble each of these modules: contextsensing, context extraction, context management,context-aware reminders, and human–computer interactions. This paper presents the details of the context managementmodule that has adopted ontological modeling and reasoning technologies. The ontological approach can support both distributed context integration and advanced temporal reasoning capabilities. iMessenger has the abilityto infer inconsistencies between what the user was expected to do and what the user is actually doing, and supply appropriate feedback to encourage people to follow their predefined agendas correctly in addition to keep healthy postures during their daily activities. The framework hasbeen validated using simulated scenarios within the Protege environment.