The newest update for Apple Watches is out now, bringing a highly anticipated feature to Series 4 devices. Apple pushed out watchOS 5.1.2 today, which includes its ECG app for monitoring irregular heartbeats.

Apple Watch Series 4 devices all have built-in electrodes that can measure electrocardiograms, or ECGs. At the time of the Watch's debut in September, Apple's native app with which the electrodes communicate wasn't ready for consumer use. Now, it's rolling out as part of the watchOS 5.1.2 update.

The ECG app is for the Watch itself, while ECG data gets stored in Apple's Health app on iOS devices. To take an ECG reading, users must place their finger on the flat side of the Digital Crown on their Series 4 Watch. The electrode on the Digital Crown communicates with the other electrode on the Watch, which sits near the heart rate monitor, to take a complete ECG measurement.

The process takes about 30 seconds to complete, and then the Watch will show your measurement as a waveform on its screen along with an explanation of what it means. Apple designed it to detect irregular heart rhythms, which could be signs of atrial fibrillation.

But even with the Series 4's FDA-clearance tag, neither the Watch nor Apple's ECG app are diagnostic tools, and they won't replace a doctor's visit. The ECG features are meant to allow users to take more control over their health and provide more background information to their doctors. The Health app even allows users to export their data as a PDF so they can more easily give it to their doctor.

The Apple Watch Series 4 stood out among previous models and competing smartwatches, thanks to the new ECG features and the new fall-detection feature. With the updated accelerometer in the Series 4, those Watches can now detect when its wearer has fallen, notifying loved ones and emergency services when the wearer cannot do so themselves.

ECG features are limited to Series 4 Watches, but Apple's irregular heart rhythm notification feature works on Series 1 devices and newer. This feature is also included in the watchOS 5.1.2 update, along with new complications for the Infograph watch face, Walkie-Talkie availability management in the Control Center, bug fixes, and more. Here are the full release notes:

This update includes new features, improvements and bug fixes: New ECG app on Apple Watch Series 4 (US and US territories only) Allows you to take an electrocardiogram similar to a single-lead electrocardiogram Can indicate whether your heart rhythm shows signs of atrial fibrillation—a serious form of irregular heart rhythm—or sinus rhythm, which means your heart is beating in a normal pattern Saves ECG waveform, classification and any noted symptoms in a PDF on the Health app on iPhone to share with your doctor

Adds the ability to receive an alert if an irregular heart rhythm that appears to be atrial fibrillation is detected (US and US territories only)

Enables direct access to supported movie tickets, coupons, and rewards cards in Wallet when tapped to a contactless reader

Receive notifications and animated celebrations when you achieve daily maximum points in a day during an Activity competition

New Infograph complications for Mail, Maps, Messages, Find My Friends, Home, News, Phone, Remote

Manage your availability for Walkie-Talkie from Control Center

Download watchOS 5.1.2 by going to the Software Update section of the General menu in the Watch iOS app. It's available for Series 1 devices and newer that are paired to iOS devices running iOS 12.1.1 and higher. You must have the Watch placed on its charger, connected to Wi-Fi or LTE, with at least 50-percent battery to download the update.