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.