Some customers have been experiencing problems using the watches if they have tattoos in the same place as the watch sits, reports CNN.
Long discussion threads on social media sites like Reddit and Twitter suggest the tattoo blocks the watch from reading a heartbeat, and the watch turns on when a heart rate is detected, so if it can’t read a heart rate, the phone won’t function properly.
“The issue stems from the way that the Apple Watch senses your heartbeat. According to Apple, the back of the Watch rapidly flashes green and infrared light at your skin, which gets absorbed or reflected by your red blood. When your heart beats, there is more blood in your wrist, and there is less blood between beats. By sensing the timing between your heartbeats, the Apple Watch can calculate your heart rate.”
This means that some tattoos, especially red ones, also “absorb the green light and reflect red light. Black tattoos, which absorb both green and red light, can also screw up the Apple Watch’s heart rate sensor.”
“The watch would lock up every time the screen went dark and prompted me for my password. I wouldn’t receive notifications,” said one commenter on Reddit.
“When I decided to try holding it against my hand (my left arm is sleeved and where I wear my watch is tattooed as well)…it worked. My hand isn’t tattooed and the Watch stayed unlocked. Once I put it back on the area that is tattooed with black ink the watch would automatically lock again,” the commenter added.
CNN reports that an Apple blog, iMore, has “confirmed the problem exists.”