A method and system for detecting atrial fibrillations from a photoplethysmogram (PPG) signal. A method includes continuously generating a PPG signal measurement from a sensor of a PPG unit; generating a plurality of time frame samples based on the PPG signal measurement; generating, for each time frame sample, a plurality of heart rate (RR) intervals; determining an RR interval distribution for each time frame sample based on the plurality of RR intervals; and detecting at least one atrial fibrillation event based on the RR interval distribution for each time frame sample.