Key Inclusion Criteria:  Fluent in spoken and written English Minimum 8 years of education or 8th grade equivalent. Willing to authorize the use of confidential health information in accordance with applicable privacy regulations. Willing to wear an Apple Watch for daily use for the duration of the study. Willing to use their personal iPhone for routine daily use for the duration of the study. Technical requirements:  iPhone models: iPhone 8 or newer iOS versions: current publicly available iOS version  Access to one of the following personal computing devices. Microsoft Windows based personal computers (laptops and desktops) Mac personal computers (laptops and desktops) Apple iPad tablets Access to WiFi or hardwired internet access in participant's place of residence. Active email address for enrollment account creation and for use in relaying study information. Active mobile telephone number for use in relaying study information when appropriate. Primary address within the United States (50 states and Washington, DC; not a post office (PO) box).  Key Exclusion Criteria:  Inability to comply with study requirements. Any self-reported medical history of dementia (such as Alzheimer's disease, frontotemporal dementia, dementia with Lewy body, vascular dementia, rapidly progressive dementia, or Parkinson's disease dementia). Self-reported dependence on others to perform core activities of daily living, including feeding, dressing, bathing, toileting, or grooming.  NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.