Inclusion Criteria:

   1. Possession of the following at time of eligibility screening:

      - iPhone (5s or later) with iOS version 12.1.1 or later defined as iPhone model/iOS
      version used to complete screening eligibility.

      - Apple Watch (Series 1-4) with watchOS version 5.1.2 or later defined as Apple
      Watch model/watchOS paired with iPhone used to complete screening eligibility

   2. At least one of the following by self-report before consent:

      - Irregular Rhythm Notification

      - ECG app classification of Atrial Fibrillation

      - ECG app classification of Inconclusive defined as "Inconclusive," "Heart Rate
      Over 120," or "Heart Rate Under 50"

   3. Age ≥ 22 years at time of eligibility screening

   4. Current resident of the United States at time of eligibility screening, and will
   reside in the United States for the length of the study

   5. Proficient in written and spoken English

   6. Valid phone number associated with iPhone, ascertained from self-report

   7. Valid email address, ascertained from self-report

Exclusion Criteria:

   1. Shared iCloud account

   2. Shared AppleWatch