The Apple Watch doesn't work as intended on tattooed arms, the tattoos confuse the wrist detection feature of the watch. The watch, available in prices ranging from $349 to $17,000 doesn't send notifications to to users wearing the device on tattooed skin.
The culprit is the watch's wrist detection feature that needs the reflection of green and infrared light to work properly. The sensor doesn't properly recognize the reflections on tattooed skin and in order to use the watch's full features, the watch has to be worn on skin that isn't tattooed.
"I thought my shiny new 42mm watch had a bad wrist detector sensor," writes user guinne55fan on Reddit, "the watch 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."
Once the user tried it on an area without tattoos, the watch worked as expected, and when put back on the tattooed part of his arm, the issues appeared again.
And what would the internet be without someone having a possible answer to why this happens? A comment on Reddit states, "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 spectrum. 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."
Apple hasn't responded on the issue so far.
