Some Apple Watch users who have tattoos are running into problems when using the device’s heart-rate monitor and other features, as it appears the ink in tattoos can interfere with the watch’s sensors.
This week, one person noted on the website Reddit that the Apple Watch’s auto-lock would engage when it was placed over an arm tattoo, possibly indicating that the device was not registering that it was being worn. And the heart-rate monitor gives different readings when placed over tattooed and nontattooed skin, with very dark ink colors appearing to cause the most trouble, according to the website iMore.
The Apple Watch monitors heart rate in the same way as the Basis Peak, the Fitbit Surge and other wrist-worn fitness trackers — they all use a light that shines into the skin to measure pulse. The light strikes the blood vessels in your wrist, and then sensors on the devices detect how much light is reflected back, which lets the devices detect the changes in blood volume that occur each time your heart beats, pushing blood through your body.
The Apple Watch has an LED light that flashes many times per second to detect your heartbeat, the company says.
However, changes to the skin, including permanent tattoos, can affect the heart-rate sensor’s performance, Apple says. “The ink, pattern and saturation of some tattoos can block light from the sensor, making it difficult to get reliable readings,” Apple’s support website states.
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