Apparently, they've discovered a problem with the new Apple Watch.
It can't read your heart rate if you have a tattoo.
Which sounds laughable, except that if it can't read your heart rate it can't tell if you're wearing it. It locks if you aren't wearing it. And disabling the autolock system also disables Apple Pay.
So, yeah. If you have wrist or sleeve tattoos on both arms, this is a problem.