Apple updated its knowledge base page for the Apple Watch to include “Permanent or temporary changes to your skin, such as some tattoos, can also impact heart-rate sensor performance,” Apple writes “The ink, pattern, and saturation of some tattoos can block light from the sensor, making it difficult to get reliable readings.” Its been suggested that mostly darker tattoos are causing the majority of issues, preventing much of the Watch’s light sensors from getting through. This isn’t just a problem related to reading heart rates. Apple also uses these sensors to detect when the Watch has been removed from a person’s arm, if the Watch doesn’t detect that it’s being worn, it won’t receive notifications, and also cause it to lock if a passcode is enabled.
Hipsters might want to test one out at the Apple store before making a purchase :)