Sensors in the Apple Watch apparently don't work like they are supposed to for users who have tattoos on their wrist where they wear their Watch. Early reports from users on Reddit and Twitter say the Watch reports inaccurate heart-rate results when placed over tattoos. It also reportedly has trouble detecting that it is on a user's wrist, which can interfere with unlocking the device and buying things with Apple Pay.

The biggest problems are being reported when the smartwatch is put up against a dark tattoo, and not so much on lighter tattoos.The problem could be that Apple Watch uses color to detect a user's pulse. The company explains the technology this way:
"Blood is red because it reflects red light and absorbs green light. Apple Watch uses green LED lights paired with light‑sensitive photodiodes to detect the amount of blood flowing through your wrist at any given moment. When your heart beats, the blood flow in your wrist — and the green light absorption — is greater. Between beats, it’s less. By flashing its LED lights hundreds of times per second, Apple Watch can calculate the number of times the heart beats each minute — your heart rate."

A Reddit user with the name of guinne55fan wrote on Tuesday that the user thought Apple had sent a defective Watch:
" I was about to give up and call Apple tomorrow 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) and 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."

So if you can't live without the Apple Watch and you have a tattoo, you may need to have the ink removed first. Or if all you care about is looking cool, you could get an Apple Watch tattooed on your arm and probably save hundreds of dollars. Check out the attached YouTube video of a tattooed user illustrating the difference in how the Watch works on a tattooed and non-tattooed arm.