Apple has just confirmed that its new smartwatch may not get along well with people who have tattoos on their wrist. The company posted an update to its support document explaining the technology behind the Apple Watch’s heart rate sensor that says certain types of ink could prevent the device from tracking a user’s heart rate.
Based on the technology behind the watch’s heart rate tracking, the limitation is hardly surprising. To measure a user’s blood flow, the watch flashes green LEDs hundreds of times every second and uses light-sensitive photodiodes to measure the absorption of that light. When someone’s heart beats, the green light absorption goes up, allowing the device to figure out when their heart is beating.
Add ink to the mix – especially dark ink, it seems – and the Watch’s ability to detect those light changes diminishes greatly. It’s not just a problem with the Apple Watch, either: other wearable devices like FitBit’s Charge HR and the Microsoft Band use similar techniques to measure a user’s heart rate.
In practice, that means some tattoo wearers won’t be able to take advantage of the heart rate tracking, or features associated with determining when a device is on a user’s wrist.
There’s good news for tattoo bearers waiting for the Apple Watch to arrive: it’s possible for buyers to return the device up to 14 days after it shows up, so long as it’s still in one piece.
