Millions of Americans own an Apple Watch, which commands roughly a 50 percent share of the smartwatch market. Among its many features, the Apple Watch can take your pulse. It also contains hardware to measure your blood-oxygen levels, and it has been doing so since the watch was released—but the hardware is not operable by the watch’s wearer, who thus cannot obtain the results. Under current FDA regulation, the function is disabled. It’s another example of how federal regulation of the production and distribution of pharmaceuticals and medical devices in the United States is less focused on stopping viruses and...