Apple has officially acknowledged that tattoos and other changes to one's skin can throw off some of the Apple Watch sensors.
More than half a year after its initial unveiling, the Apple Watch finally went on sale recently, albeit in rather limited supply. Some of those who did manage to get their hands on an Apple Watch, however, reported that tattoos can have a negative impact on the accuracy of some sensors found on the Apple Watch. More specifically, the heart rate sensor will be tricked by the ink in the tattoo, and the reading will not be accurate.
"The heart rate sensor in Apple Watch uses what is known as photoplethysmography. This technology, while difficult to pronounce, is based on a very simple fact: 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," Apple explained.
"The heart rate sensor can also use infrared light. This mode is what Apple Watch uses when it measures your heart rate every 10 minutes. However, if the infrared system isn't providing an adequate reading, Apple Watch switches to the green LEDs. In addition, the heart rate sensor is designed to compensate for low signal levels by increasing both LED brightness and sampling rate."
Following multiple reports of tattoos affecting the Apple Watch sensors, Apple has now officially acknowledged the issue. In an update to its support page, Apple has now noted that the heart rate sensor of the Apple Watch may not work well with tattoos.
"Permanent or temporary changes to your skin, such as some tattoos, can also impact heart rate sensor performance. The ink, pattern, and saturation of some tattoos can block light from the sensor, making it difficult to get reliable readings."
The company further suggests that if Apple Watch wearers cannot get a consistent reading from the gadget because something (such as tattoos) is affecting the sensors, they can connect the gadget wirelessly to external heart rate monitors such as Bluetooth chest straps.
Bottom line, if you have a tattooed wrist and are planning on purchasing an Apple Watch, you might want to try out the smartwatch in the Apple Store before making your purchase.
