Irked Apple fans have dubbed the issue "TattooGate" on Twitter, complaining they must choose between their body art and their stylish gadget. Apple, for its part, acknowledged the issue on its support website.

"Permanent or temporary changes to your skin, such as some tattoos, can also impact heart rate sensor performance," the site reads. "The ink, pattern, and saturation of some tattoos can block light from the sensor, making it difficult to get reliable readings."

Several watch owners complained about the problem on social media this week, even posting videos that show the watch working well on an undecorated wrist, but repeatedly locking or pausing when worn on an arm with a tattoo. Some said it appeared the watch's screen-lock feature was triggering because the sensors thought the watch was not sitting on their wrist.

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That was frustrating and "a bit embarrassing" for Graham Edgell, a Los Angeles printing broker who loves Apple products and was eager to show off his new watch to friends after his wife bought it for him. Edgell, 38, said he thought a software glitch was interfering with the watch's message notifications and other features, until he heard about others having trouble with their tattoos.

Edgell solved his problem by moving the watch further down on his wrist, away from the dark floral tattoo that stops just above the cuff of his shirt sleeve. "When it was on the tattoo, it was as if it had lost connection with my skin," he said. "Now it's absolutely fine," he added.

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The watch tracks heart rates through a common medical technique that measures how much light is absorbed by blood.

An Apple representative referred a reporter to the company's website, which explains "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."