Systems, methods, and computer software for detecting atrial fibrillation are described. Photoplethysmographic (PPG) signal data may be received as communicated by a PPG sensor of a wearable device worn by a user. Heartbeats from a portion of the PPG signal data may be determined and a heart rhythm type may be determined based on at least the heartbeats. A determination of whether the heart rhythm type includes Atrial Fibrillation (AF) may be made, and, when AF is detected, an AF detection alert may be displayed at the wearable device.