A method includes receiving heartbeat data of a patient and receiving activity data of the patient. The activity data includes one or more activity values that are related to an activity level of the patient and that are measured independently of the heartbeat data. The method further includes determining a value of a weighting factor based on the activity data. The method also includes determining modified heartbeat data by applying the weighting factor to at least a portion of the heartbeat data. The method also includes detecting a seizure event based on the modified heartbeat data.