Tattoos may stop Apple Watch from working

Want an Apple Watch? Have a wrist tattoo? You may have a problem.

It seems tattooed wrists can prevent the Apple Watch's heart rate sensor from functioning properly.

Maybe not a huge problem, until you consider the watch uses the heart rate function to determine if you’re wearing it for functions such as Apple Pay, to place calls, receive notifications and more.

CNNMoney reports the issue stems from the way the Apple Watch senses your heartbeat. 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. 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.

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