Apple Watch running the original 1.0 software rather reliably recorded a user’s heart rate every ten minutes. With Watch OS 1.0.1, users noticed that heart rate records were no longer being kept as frequently. This was initially thought to be a bug but Apple has now clarified that this is intended behaviour on its website.

The updated website says that ‘Apple Watch attempts to measure your heart rate every ten minutes, but won’t record it when you are in motion or your arm is moving’. The original version of this feature did not care about arm movement.

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This has caused some complaints from users who thought that the original Watch software recorded heart rate without any issues whatsoever and now see the device as losing functionality with the software update.

It is unclear why Apple has made this change in behaviour, arguably a regression in functionality. There has been some speculation that Apple changed this behaviour to conserve battery life but again this has only angered users who did not see any adverse battery drain from the regular every-ten-minute monitoring.

To offer some fix for the problem, users can still start a workout in the Workout app to force continuous heart rate monitoring by the system, which will record heart rate measurements about every ten seconds. The downside to this is that users have to remember to activate this mode explicitly unlike the passive monitoring.

Update: Following some confusion, it’s worth noting that the ‘arm is moving’ does not affect the heart rate detection used by the Workout app. This is because the Workout app uses the green LEDs and photo sensors to detect heart rate, whereas the passive heart rate monitoring uses only infrared sensors. Apple is not letting the infrared sensors record readings if a user’s arm is moving with the latest Apple Watch software update — the behaviour of the continuous heart rate monitoring when using the Workout app remains the same.