If you are deciding to get a sleeve tattoo and then buying an Apple Watch at the same time (what are the odds), here is a reason to think again. Users from Reddit, Twitter and other social media are reporting that the Apple Watch is not able to read heartrates properly and loses connection when worn over a tattoo.
The smartwatch requests for your security pin every single time it detects itself leaving your wrists, so this issue can be very annoying. Imagine having to key in your pin every single time. Even iMore, a weblog for all things Apple confirms the problem on inked wrists.
According to iMore, lighter coloured tattoos seem to give the least problems with only having trouble reading a proper heartrate and patterned tattoos showed no error, but this may vary from user to user.
There is a very good explanation to why this is happening, which is explained by Apple here :
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 problem is shared among several other fitness bands including the Fitbit’s Charge HR and the Microsoft band but here is a solution to the problem. Since Apple Watch is compatible with some popular Bluetooth heart rate chest straps such as the Polar H7, you could instead use those or wait for a software update.
[Source: The Verge]