Apple has released watchOS 5.1.2, the software update that enables the ECG (electrocardiogram) feature on the Apple Watch Series 4. The new feature is designed to measure electrical activity of the heart in order to capture heart rhythm and possibly detect symptoms of life-threatening conditions.

The feature is only available in the United States, including Puerto Rico, Guam and the U.S. Virgin Islands. MacRumors reports that switching the region on Apple Watch devices sold outside the U.S. won’t enable ECG. Some previously released Apple software can be tricked by using this method, but Apple has made sure that this won’t happen this time around.

The ECG feature on the Apple Watch can be accessed through the dedicated app, which should already be installed on the smartwatch after updating to watchOS 5.1.2. Users are required to have an iPhone 5s or newer device running iOS 12.1.1 with Apple’s Health app installed. Users will need the Health app in order to set up the ECG feature on the Apple Watch.

Once the ECG has been set up through the Health app, users can now open the ECG app on the Apple Watch. The app will instruct users to place a finger on top of the Digital Crown of the Apple Watch. Users should make sure their finger is placed on top of the Digital Crown because the built-in electrode is located there and not on its sides.

Users will have to keep their finger on the Digital Crown for 30 seconds while the app measures their heart rhythm. The Apple Watch should display a countdown timer during this process, so users can easily tell if the process has been completed. Once the the Apple Watch is done taking the ECG measurement, it will show the user a heart rhythm classification which can be shared with their doctor.

If the ECG app detects a normal rhythm, users will be informed that they have a standard sinus rhythm. If the app detects an abnormal heart rhythm, it will tell them that it has detected atrial fibrillation and Apple will recommend seeing a doctor for professional help.

The ECG app will save the waveform, classification and any other information gathered from the measurement onto the iPhone Health app, according to AppleInsider. The Health app will also provide the user an option to easily turn the relevant information into a PDF file and send it directly to their doctor.

The ECG feature on the Apple Watch could help users know if they have any heart conditions. However, it’s important to point out that the Apple Watch Series 4 is only able to take a single-lead electrocardiogram, which isn’t as sensitive as what doctors use in hospitals. That said, the Apple Watch should still be able to accurately classify atrial fibrillation and sinus rhythm.

Apple Watch 4 Apple just released watchOS 5.1.2 and it enables the ECG feature on the Apple Watch 4. Photo: NOAH BERGER/AFP/Getty Images