Apple Heart Study: Assessment of Wristwatch-Based Photoplethysmography to Identify Cardiac Arrhythmias

Inclusion Criteria:

Possession of the following at time of eligibility screening, ascertained from automatic hardware/software/device pairing check:

* iPhone (5s or later) with iOS version 11.0 or later defined as iPhone model/iOS version used to complete screening eligibility.
* Apple Watch (Series 1 or later) with watchOS version 4.0 or later defined as Apple Watch model/watchOS paired with iPhone used to complete screening eligibility.
* Current resident of the United States at time of eligibility screening, defined by self-reported state of residence within the 50 states of the United States or District of Columbia.
* Proficient in written and spoken English, defined by self-report of comfort reading, writing, and speaking English on iPhone.
* Valid phone number associated with iPhone, ascertained from self-report.
* Valid email address, ascertained from self-report.

Exclusion Criteria:

* Self-reported diagnosis of Atrial Fibrillation.
* Self-reported diagnosis of Atrial Flutter.
* Currently on anti-coagulation therapy.