Apple Updates Technical Document to Explain Apple Watch Heart Rate Sensor Errors

I recently wrote about how the Apple Watch doesn’t record heart rates correctly. Lots of users are seeing this problem, and, previously, Apple’s documentation about this claimed that the heart rate sensor recorded heart rates every 10 minutes.

Now, Apple has 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.

This is quite surprising. Why wouldn’t it take a reading when you’re in motion? After all, the goal of a fitness tracker is to motivate you to be active. This means that the Apple Watch cannot make any claim to realistically calculate your activity based on your heart rate. It will only measure your heart rate (if you’re moving) if you’ve initiated a workout with the Workout app; in which case it checks your heart rate more or less continuously. And if it’s not reliable when you’re moving, then how can they claim it’s reliably when you’re doing a workout?

It may be that Apple made this change – the heart rate sensor did check every ten minutes before the WatchOS 1.0.1 update – to save battery power. But it seriously compromises the Apple Watch’s ability to track your fitness.

It’s also interesting that Apple’s support team wasn’t aware of this. They exchanged my Apple Watch because of the heart rate sensor not recording regularly, and not recording reliably (which still happens).

Here’s how that technical document looked on May 9 (via the Wayback Machine):

Heart rate tech doc

In short, Apple discovered that the heart rate sensor wasn’t reliable enough in real-world use. They decided to turn it off, unless one is at rest or doing a workout. It seems that the heart rate sensor is essentially useless, unless you use the Workout app. In essence, other than for workouts, the Apple Watch, as a fitness tracker, is no different from one that simply counts steps.

14 thoughts on “Apple Updates Technical Document to Explain Apple Watch Heart Rate Sensor Errors

  1. Obviously this is battery related. The infrared sensor doesn’t work as well as the green light sensor which is used during workouts. I just don’t understand the reluctance to use the workout app.

    • You obviously don’t understand the issue. You can’t use the workout app for passive HR monitoring since it records every 5 seconds and yes it would deplete the battery in about 5-6 hours.

      The issue is that passive monitoring was promised at 10 minute intervals while “not” working out. Passive monitoring is critical to gauge training recovery, resting HR, etc. Apple basically removed passive monitoring with the 1.0.1 update.

      Apple should let the user manage battery life and not impose solutions on those who want to use the AW as more of a training/fitness device in exchange for having to charge it more often.

      If you want great battery life, just turn it off .. you have that option. I would like to have the option to use the HR monitor in a fashion that makes the AW a 24-hour training tool. Options are good.

  2. Obviously this is battery related. The infrared sensor doesn’t work as well as the green light sensor which is used during workouts. I just don’t understand the reluctance to use the workout app.

    • You obviously don’t understand the issue. You can’t use the workout app for passive HR monitoring since it records every 5 seconds and yes it would deplete the battery in about 5-6 hours.

      The issue is that passive monitoring was promised at 10 minute intervals while “not” working out. Passive monitoring is critical to gauge training recovery, resting HR, etc. Apple basically removed passive monitoring with the 1.0.1 update.

      Apple should let the user manage battery life and not impose solutions on those who want to use the AW as more of a training/fitness device in exchange for having to charge it more often.

      If you want great battery life, just turn it off .. you have that option. I would like to have the option to use the HR monitor in a fashion that makes the AW a 24-hour training tool. Options are good.

  3. Kirk, You’ve made a valiant public effort, but might it be time to take it back citing “not fit for purpose” or even misleading advertising/claims…?

  4. Kirk, You’ve made a valiant public effort, but might it be time to take it back citing “not fit for purpose” or even misleading advertising/claims…?

  5. Geez Kirk, and pardon the sarcasm, but I got caught again today with Synch Errors. Of course I was not he way to the airport.

    Not that it’s related, but if Apple cannot keep track of what’s available/used when synching my iPad accurately, how can it possibly keep track of my heart when it fluctuates based on activity and environment (airport and crowd negotiation).

  6. Geez Kirk, and pardon the sarcasm, but I got caught again today with Synch Errors. Of course I was not he way to the airport.

    Not that it’s related, but if Apple cannot keep track of what’s available/used when synching my iPad accurately, how can it possibly keep track of my heart when it fluctuates based on activity and environment (airport and crowd negotiation).

  7. I too was concerned when I first read the revised technical document, but from what I am seeing on my iPhone in the Health app, the Watch is indeed still recording a reading every ten minutes without fail. I’m wondering if the document is simply implying that the Activity app is not recording the reading. Not sure why that would be, but it is definitely recording readings every 10 minutes on my device. In fact, I can scroll back to prior to the update, and I see no difference in the frequency of the HR entries.

    • Did you apply the 1.0.1 software update to your Apple Watch? Because unless you’re not moving at all, you shouldn’t be seeing regular updates.

      • Yes, I had it installed within a few hours of its release. I will say that today has been less than every 10 minutes, but it has been consistently capturing data all day – several times per hour at a minimum. I’ve been working at my desk most of the day, but haven’t been intentionally motionless at all. In fact, I’ve been doing a lot of typing, and have only been prompted to stand twice today.

  8. I too was concerned when I first read the revised technical document, but from what I am seeing on my iPhone in the Health app, the Watch is indeed still recording a reading every ten minutes without fail. I’m wondering if the document is simply implying that the Activity app is not recording the reading. Not sure why that would be, but it is definitely recording readings every 10 minutes on my device. In fact, I can scroll back to prior to the update, and I see no difference in the frequency of the HR entries.

    • Did you apply the 1.0.1 software update to your Apple Watch? Because unless you’re not moving at all, you shouldn’t be seeing regular updates.

      • Yes, I had it installed within a few hours of its release. I will say that today has been less than every 10 minutes, but it has been consistently capturing data all day – several times per hour at a minimum. I’ve been working at my desk most of the day, but haven’t been intentionally motionless at all. In fact, I’ve been doing a lot of typing, and have only been prompted to stand twice today.

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