Perhaps the biggest hardware release since the iPhone, gadget enthusiasts everywhere highly anticipated the Apple Watch’s release. One of its noteworthy features is the heart rate monitor, which uses a device called the "pulse oximeter" that emits infrared light through a user's wrist to measure the oxidation of their blood. The oximeter determines a user's heart rate based on how much light is absorbed through the skin and blood cells. The problem with this technology, however, is that it doesn’t work on dark or tattooed skin.
During product testing, only Apple executives are allowed access to teams involved in the development. So in the Apple Watch's case, it's possible that executives—the top 10 of whom are all white—didn't consider testing on a variety of skin types early on. Although the company addressed the tattoo issue, which also affects Apple's heart-rate monitor, it has yet to mention the device's issue with darker skin.