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Apple Watch won't work properly on some tattooed wrists

Apple Watch won't work properly on some tattooed wrists


The ink messes with Apple's heart rate sensor

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If you need another reason to rethink getting that sleeve tattoo, Apple just gave you one: the Apple Watch doesn't work so well when worn on a tattooed wrist. A few days after the smartwatch's launch, users on Reddit, Twitter, and other social media channels are reporting that the Watch loses connection and reports inaccurate heart rate results when placed over tattoos. The video embedded above is a pretty effective demonstration.

Such an issue could quickly prove annoying, since Apple Watch requests a security PIN almost immediately after it detects it has left an owner's wrist. Here, that's happening while it's still securely strapped on. iMore has already conducted some pretty thorough tests and found that yes, Apple's watch can run into significant problems on inked customers.

Read next: Read our Apple Watch review.

Dark, solid colors seem to give the sensor the most trouble — our tests on solid black and red initially produced heart rate misreadings of up to 196 BPM before failing to read skin contact entirely.

Tattoos with lighter colors seemed to give Apple Watch less trouble, only leading to heart rate readings that were slightly off the mark. As for patterned tattoos, iMore's tests showed no errors, but this can obviously vary wildly depending on a specific tattoo design.

Apple Watch heart rate

Apple warns of potential problems on its website, but doesn't specifically mention tattoos.

But when you consider how Apple Watch gets those heart rate readings, this problem shouldn't be very surprising. Here's how the company explains the technology:

Blood is red because it reflects red light and absorbs green light. 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. Between beats, it’s less. By flashing its LED lights hundreds of times per second, Apple Watch can calculate the number of times the heart beats each minute — your heart rate.

This approach is one shared by other fitness bands including Fitbit's Charge HR and the Microsoft Band. The ink from a tattoo can dramatically complicate things for these devices in ways that natural human skin pigmentation never would. On the same page where it offers technical details on the heart rate sensor, Apple also says, "For a small percentage of users, various factors may make it impossible to get any heart rate reading at all." Apple should probably amend this page and make it more obvious that tattoos could present a problem.

This isn't a problem unique to Apple Watch.

The heart rate solution is simple enough; since Apple Watch is compatible with popular Bluetooth heart rate chest straps like the Polar H7, you can simply use one of those to get an accurate reading during workouts. But that doesn't solve the issue of Apple Watch mistakenly thinking it's not on a wrist in the first place, which presents a much bigger headache. Perhaps Apple can fine tune these skin detection algorithms in a future software update. But for now, like iMore says, you'll definitely want to visit the Apple Store for a fitting to test things out before spending at least $350 on an Apple Watch of your own.