Family setting in watchOS 7 lets your relatives who do not own an iPhone enjoy the health features of the Apple Watch. But families buying the new Series 6 Apple Watch for Grandma may face a serious annoyance ̵1; it turns out that the Series 6’s selling point, its blood oxygen monitor, is disabled on Apple Watches running in the Family Setup system.
Apple’s support page states that “The Blood Oxygen app is not available if you set up your Apple Watch with Family Setup.” But the company has not clarified why Family Setup disables the blood oxygen monitor. Is it a hardware restriction, or is Apple trying to stop people from using its non-FDA-approved blood oxygen app for “medical” purposes?
The Blood Oxygen app is not available for people under the age of 18, even if they own their own iPhone. Apple keeps track of users’ ages through the Health app, which asks for a date of birth during installation.
Enabling Family Setup on a relative’s Apple Watch does not affect the features of your iPhone or Apple Watch. This restriction only affects family members who use a Series 6 Apple Watch without their own, personal iPhone. Other health monitoring features, such as fall detection and ECG, are not affected by Family Setup.
Source: Apple via MacRumors