The result? People with tattoos don't get notifications, unless they move the Watch to an un-tattooed³ area, or turn off wrist detection. Not exactly ideal for those with full sleeves! 

 

"I thought my shiny new 42mm [Watch] had a bad wrist detector⁴ sensor," writes one user. "The [W]atch would lock up every time the screen went dark and prompted me for my password. I wouldn't receive notifications. I couldn't figure out why especially since the watch was definitely not losing contact with my skin. [A]lso I couldn't find anything online with people experiencing this issue. I was about to give up and call Apple … when I decided⁵ 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." 

 

As a possible explanation, another Redditor writes that: 

 

"Oxyhemoglobin has several local peaks of absorbance which can be used for pulse oximetry: one green, one yellow, one infrared, etc. Apple uses the ones at infrared and green parts of the spectrum⁶. Now, here's some key facts. Melanin and ink are both equally good at absorbing frequencies over 500nm, which sadly includes the green. But, melanin's absorbance falls down so rapidly that by the infrared end of the spectrum its hardly absorbing anything at all. That, combined with the fact that Apple adjusts the sensitivity/light level dynamically means infrared is probably black people friendly. Ink has a much more gradual fall off, so even infrared might not work for them." 

 

While it's possible to turn off the wrist detection feature, this also stops Apple Pay from working. We've reached out to Apple to ask if this is a problem that's been reported elsewhere, and will update this post when we hear back.

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