Apple Watch heart monitor woes confirmed by Apple

AppleWatchAs with any new device, the Apple Watch has had its share of complaints from users who expected some functionality and found the device does not live up to expectation. In a recent support document update for the Apple Watch, Apple acknowledges one drawback, where the device may be unable to perform proper biometrics on inked skin. This results in those with tattoos and similar color changes on their wrists, finding the watch’s heart rate monitor will not detect beats, and claim they have zero heart rate.

The heart rate sensor on the Apple Watch works by detecting pulsing color changes caused by light absorption and reflectance changes that occur in your skin. As blood is pumped from your heart, the resulting pulse will produce a rush of blood through the capillary beds of your skin, changing its spectral properties.

The Apple Watch detects this by using green and infrared LEDs to illuminate this effect and amplify the spectral changes in your skin with each heart beat. These changes are then picked up by two photodiodes that can detect the difference between skin with less blood and that containing a wave of blood from a heart pump.

The use of spectral responses for this means that if you have a color in your skin that will absorb the light emitted from the watch, then your skin may not emit enough of a spectral difference between heartbeats for the watch to detect. This is likely more of a problem with darker pigments, that may still absorb enough to block the sensor, even as the watch adjusts its LED brightness to compensate. As a result, the issue may not happen on lighter tattoos or other markings, but may happen prominently on skin that is heavily inked, including black and red ones, and especially on complex patterns of ink.

Unfortunately besides waiting for a software update that refines its ability to use the LEDs and sensors to accurately detect pulses through inks that might absorb its detecting lights, there is little that you can do to fix this issue. The only options you have are to wear the watch differently, and especially ensure that it is snugly strapped to your wrist.

Apple Watch heartbeat sensor schematic

The Apple Watch uses LEDs to emit green and infrared light that will help detect spectral changes in your skin during heartbeats. However, the effect may be dampened in inked skin, and for those who have low perfusion through the skin on their wrists (image credit: Apple).

In its support document, Apple also outlines other details that might affect the performance of the heart rate monitor, including low blood flow from a cold environment or if you on average have generally less blood flow in your skin. Apple also mentions the heart rate monitor may be affected by very active and irregular movements, such as playing rigorous tennis.

7 thoughts on “Apple Watch heart monitor woes confirmed by Apple

    1. Topher Kessler Post author

      There may or may not be one, but for now we can only wait and hope an update refines how the sensors are used, and returns some functionality for those who are affected.

  1. venicejeff

    i’m all for tattoos if you want them. but when getting one, you choose to get all that comes with it. not apple’s fault. you get tattoos to change other’s perceptions of you, and it changes the watch’s perception too

    1. B. Jefferson Le Blanc

      It may not be Apple’s fault that you have a tattoo on your wrist, but they could have foreseen the problem and worked out a solution ahead of time. Alternatively, they could have, and should have, disclosed the issue ahead of time so that people considering getting an Apple Watch could weigh the fact in their buying decision. At a minimum the problem may move some people to return their Apple Watches or cancel their orders. Apple’s failure to disclose the problem in a timely manner may encourage others to consider a class-action lawsuit. Though here the issue may be the definitions of “timely” and “disclose.”

      A problem like this further suggests that anyone thinking of buying an Apple Watch go to an Apple store and try one on first to see how it works on their own wrist.

      On the up side, I really like the Apple Watch TV ads, even though I won’t be getting a watch myself.

  2. Jack Thomas

    Your mother was right. You shouldn’t have gotten that tattoo. Not only do you look like a complete jacka$$, your expensive Apple Watch doesn’t work!

  3. BenG

    It also won’t work over a shirt cuff, or lying on the table. People who have tattoos have destroyed a part of their skin (whole body tattoos cause kidney failure), so they deserve what they get.

  4. Martin Cohen

    Wow – look at the tattoo haters! I don’t have any tattoos and don’t plan to get any, but I have absolutely no problems with other people getting them. I guess Apple didn’t have people with tattoos in the test program.

    I like my Pebble, anyway – it’s good enough for me.

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