“Apple changed the way the heart rate sensor works on the Apple Watch, changing a technical document that describes the feature, changing the way this feature is described for the Apple Watch,” Kirk McElhearn writes for Kirkville. “Apple updated a technical document about how the heart rate sensor works. They are no longer saying that the Apple Watch reads your heart rate every ten minutes; instead, they say this: ‘Apple Watch attempts to measure your heart rate every 10 minutes, but won’t record it when you’re in motion or your arm is moving.'”

“I think the problem is in the accuracy of the heart rate sensor. As Apple’s technical document explains, the Apple Watch has two types of heart rate sensors. ‘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,'” McElhearn writes. “These sensors are used when you are in workout mode. But the device also has other sensors: ‘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.’ While it’s a bit ridiculous that this part of the document still talks about 10-minute readings, what’s important to note is that these readings, which seem to be less accurate, are using a different sensor. It seems that Apple found these readings to be unreliable, and simply turned them off.”

“To many users, it looks like Apple pulled a bait-and-switch, promising a certain feature and not delivering it. Apple needs to say whether the change is because of faulty heart rate sensors – which means they have a bigger issue – or because of battery life. And if it’s the latter, they should allow users to choose whether or not the Apple Watch checks their heart rate every ten minutes. Let users decide how they want their battery usage to work,” McElhearn writes. “However, if the heart rate sensors are faulty, simply turning them off, after promising this feature, is a mistake. They should fix them, whether through a software update, or by exchanging the devices. They promised a feature, and they can’t simply pretend that they never did so.”

Read more in the full article here.

MacDailyNews Take: Apple needs to clarify exactly what’s happened here or face the inevitable – and justified – class action lawsuit(s).

Apple’s original heart rate support document stated, in part:

The average heart rate is 72 beats per minute (bpm). As you exercise, your muscles need more oxygen, and your heart beats faster to deliver it. During workouts, the heart rate sensor in Apple Watch measures your heart rate and displays it right on your wrist. You can also check your heart rate at any time using the Heart Rate Glance. And throughout the day, Apple Watch measures your heart rate every 10 minutes and stores it in the Health app. All this information, as well as other data it collects, helps Apple Watch estimate how many calories you’ve burned. And by checking your heart rate during workouts, you can see how both your intensity level and your heart rate change over time.

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.

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.

Apple’s latest Apple Watch heart rate support document, modified on May 30, 2015, now states in part:

You can check your heart rate any time using the Heart Rate Glance. And when you’re using the Workout app, Apple Watch measures your heart rate continuously during the workout. This information, as well as other data it collects, helps Apple Watch estimate how many calories you’ve burned. In addition, Apple Watch attempts to measure your heart rate every 10 minutes, but won’t record it when you’re in motion or your arm is moving. Apple Watch stores all your heart rate measurements in the Health app.

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. In addition, the heart rate sensor is designed to compensate for low signal levels by increasing both LED brightness and sampling rate.

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.

Even under ideal conditions, Apple Watch may not be able to get a reliable heart rate reading every time for everybody. And for a small percentage of users, various factors may make it impossible to get any heart rate reading at all.

SEE ALSO:

Heart health app seeing big usage on Apple Watch – May 14, 2015
Apple Watch heart rate data vs. Mio dedicated heart rate monitor – May 7, 2015
Apple Watch once again shows skin tone not a new issue for heart monitors – April 30, 2015
Apple explains Heart Rate on Apple Watch technology – April 20, 2015