Tattoos And Apple Watch Don't Like Each Other And Here's Why

Some users with full sleeve tattoos have been complaining that their tattoos interfere with the Apple Watch's heart rate sensor and skin contact registration. Some users with tattoos also have been unable to receive notifications and are frequently prompted to re-enter their passcode.

A Reddit thread, discussing the issue has already received more than 700 upvotes and 300 comments since being posted on Tuesday.

"So I thought my shiny new 42mm SS watch had a bad wrist detector sensor," writes Reddit user guinne55fan. "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. also I couldn't find anything online with people experiencing this issue. I was about to give up and call Apple tomorrow when I decided 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."

The reason behind this behavior is the way Apple Watch works.

The issue stems from the way that the Apple Watch senses your heartbeat. According to Apple, the back of the Watch rapidly flashes green and infrared light at your skin, which gets absorbed or reflected by your red blood. When your heart beats, there is more blood in your wrist, and there is less blood between beats. By sensing the timing between your heartbeats, the Apple Watch can calculate your heart rate, noted WTVR.com.

As it turns out, solid-colored tattoos - particularly red ones - also absorb the green light and reflect red light. Black tattoos, which absorb both green and red light, can also screw up the Apple Watch's heart rate sensor.

Apple is yet to provide comment on the matter.