1. A method comprising: receiving heartbeat data of a patient; receiving activity data of the patient, wherein 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; determining a value of a weighting factor based on the activity data; determining modified heartbeat data by applying the weighting factor to at least a portion of the heartbeat data; and detecting a seizure event based on the modified heartbeat data.