The goal of this study is to validate the Fitbit ECG software algorithm's ability to detect atrial fibrillation using data derived from a Fitbit wrist-worn consumer device that features a single lead ECG. The performance of the software application will be measured against centralized Core Lab physician-adjudicated 12-lead ECG tracings from FDA cleared ECG monitors as reference standards. The Fitbit software is intended as a pre-screening technology. It should identify candidates who may benefit from further evaluation. The software is not intended to be a diagnostic system.

Inclusion Criteria:

• Women and men 22 years of age or older
• Capable of giving informed consent
• Sufficient manual dexterity to capture an ECG from the Fitbit wrist-worn device.
• Subjects in the atrial fibrillation (AF) cohort must have a known history of AF and must be in -AF at the time of enrollment based on the screening ECG

Exclusion Criteria:

• Anti-arrhythmic (rhythm control) medication use (such as amiodarone or flecainide)
• Cardiac pacemaker or implantable cardioverter-defibrillator
• History of a life-threatening rhythm such as ventricular tachycardia or ventricular fibrillation
• Subjects in the sinus rhythm (SR) cohort should not have any history of atrial fibrillation and should not be in atrial fibrillation or other atrial arrhythmia at the time of enrollment based on the screening ECG

Subjects will be recruited at the individual clinical sites. Subjects may be recruited during routine clinic visits or may be asked to come in specifically for this study.