Have an Apple Watch Series 4? The built-in electrodes let you take an electrocardiogram from your watch if you’re at least 22 and live in the United States, but they can also improve general heart rate readings — regardless of where you live.

Just launch the Heart Rate app on the Apple Watch Series 4 running the latest software update and put your finger on the Digital Crown during the heart rate reading. This allows the Heart Rate app to switch from infrared light-based measurements to using the electrodes on the electrical heart rate sensor behind the watch and in the Digital Crown.

According to Apple, putting your finger on the Digital Crown to capture a heart rate reading also measures faster and with more accuracy as it updates every second versus every five seconds while the measurement is active.

When you place your finger on the Digital Crown, it creates a closed circuit between your heart and both arms, capturing the electrical impulses across your chest. To use the electrical heart sensor to measure your heart rate, open the Heart Rate app and place your finger on the Digital Crown. You will get a faster reading with higher fidelity — getting a measurement every second instead of every 5 seconds.

Measuring heart rate with electrodes versus infrared light requires Apple Watch Series 4 with the upgraded heart rate sensor and Digital Crown, but you don’t have to purchase your watch from the United States as you do with the FDA-regulated ECG app.

That means you can benefit from the built-in electrodes on Apple Watch Series 4 regardless of where you live without waiting for government agencies to approve a specific feature.

When you record your heart rate using this method, the Health app on the iPhone will note that the measurement was captured using the electrodes by denoting ‘ECG’ as the source (versus sedentary, background, workout, etc.). This lets you identify which measurements were captured using infrared light every five seconds versus electrodes every second.

Learn more about the Apple Watch heart rate sensor here.

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