Early adopters of the new Apple Watch have found that the device malfunctions when worn by people with wrist tattoos.
The issue was first pointed out on social media site Reddit by a tattooed user who complained that his watch would regularly lose connection, and report inaccurate heart rate results.
Scores of other users then reported similar issues.
Apple Watch requests a security PIN immediately after detecting that it has left an owner’s wrist, meaning that those affected are forced to repeatedly enter their code.
Darker tattoos appear to cause more problems for the device than light inkings.
The problem should have been foreseeable – Apple has already explained that it measures heart rate by analysing light absorption through the skin.
The Reddit user who first flagged up the problem wrote: “So I thought my shiny new watch had a bad wrist detector sensor.
He said that the watch would lock up every time the screen went dark and prompted for a password. He then decided to try holding it against his hand and it worked.
The watch stayed unlocked the whole time but once put back on the tattooed arm it automatically locked.
The wrist detection feature can be turned off, but it stops Apple Pay from working.
Apple has not yet commented officially on that issue.