Aetna provided a clue as to how the Watch would be used by writing that its own employees "will participate in the company's wellness reimbursement program, to encourage them to live more productive, healthy lives." It could presumably also also collect detailed health and fitness data to help refine its actuarial tables and other insurance data, assuming user opt-in.

Aetna will be the first major health care company to subsidize a significant portion of the Apple Watch cost, offering monthly payroll deductions to make covering the remaining cost easier.

Apple also has a ResearchKit program that helps scientists relate heart-rate and other health data to cancer, heart disease and other maladies. It recently signed up the first major drug company, GlaxoSmithKline, which will use it for a rheumatoid arthritis study.

Apple has been working hard to getting its HealthKit app into the US health care system, so Tim Cook is understandably "thrilled" with the cozy relationship. An Aetna spokesperson told Ars Technica that "Apple will have employees devoted to providing support to Aetna on this initiative [and] ... will also have a dedicated employee unit focused on this collaboration." The Watch Series 2 may have convinced the insurer to get onboard, since it's more focused on health and fitness than the original model.