Apple Watch Ultra 4 keeps the 49mm titanium case and pushes the endurance story further: up to 50 hours of normal use, 84 hours in Low Power Mode, and up to 45 hours of Max Extended Workout tracking - enough GPS-and-heart-rate logging for a 100-mile race. It also adds built-in satellite messaging for when cellular and Wi-Fi are gone, and it shares Series 12's Health Sensing System: heart rate every five seconds, denser HRV, and a 0-10 readiness score. Apple still activates it through iPhone. Merge is the Android companion: one activation, then Ultra 4 pairs to your Android phone with notifications, Google Fit sync, and an encrypted connection that can actually last as long as the battery.
What Merge adds on Ultra 4
Satellite, dual-frequency GPS, the Action button, and WR100 water resistance already work without a phone. Merge covers the Android side that Apple leaves out. Notifications from Android apps show up in real time on the 49mm display, with per-app filters so a long trail day does not become a notification storm. Replies and quick actions stay on the watch. Music on the Android phone is controllable from the wrist, and Find My rings either device.
Workouts, heart rate, sleep, steps, and calories sync to Google Fit and Health Connect; ECG history lands in the Merge Android app. Ultra 4's claim of the most accurate sports-watch GPS and the most accurate step tracking of any smartwatch is only useful on Android if that data actually arrives - Merge is what files it. Readiness and the higher-frequency heart-rate stream stay on the watch and then follow into Fit once the pair is up.
Because Ultra 4 can stay awake for two days of normal use, the encrypted Merge connection matters more than on a 24-hour Series watch: Bluetooth nearby, internet when you split up, and Smart Hotspot when the watch leaves Wi-Fi. Merge handles the hotspot without a manual switch, which is the difference between a watch that goes quiet in the backcountry and one that still delivers messages until satellite takes over.
One-time iPhone activation
Ultra 4 is no exception to Apple's activation rule: an iPhone is required once, then you can put it aside.
Ultra 4 runs watchOS 27, so you need an iPhone 11 or later or iPhone SE (2nd generation or later) with iOS 27 or later. Own the iPhone? Pair through the Watch app as usual. Borrowing? Use Set Up for a Family Member, sign the watch into your Apple ID, and place both Apple IDs in Family Sharing - the setup flow can create that group. After activation, watchOS updates install on the watch from Settings - General - Software Update on Wi-Fi. You do not bring the iPhone back for software updates.
Installing Merge
Install Merge on the phone and the watch first - pairing needs both.
- Search Google Play on your Android phone for Merge Watch and install it.
- On Ultra 4, open the App Store, find Merge Watch, and install it.
Pairing Ultra 4 to Android
Keep the watch a couple of feet from the phone while they exchange the PIN - the 49mm radio is strong, but first pairing is still a close-range step.
- Start Merge on Android and grant each permission it requests.
- With the phone app still in the foreground, open Merge on Ultra 4 and allow Bluetooth.
- Select your Android phone from the list on the watch.
- Enter the watch PIN on the phone. Pairing is done in seconds.
- Set up a Merge subscription if you don't have one yet.
- On Ultra 4, approve notification access and health permissions.
- Do the same health approval on Android.
Day-to-day with Ultra 4 on Android
Fifteen minutes on the charger returns up to 18 hours of use, so a pre-dawn top-up covers a long race day. Max Extended Workout tracking stretches GPS and heart-rate logging to 45 hours; standard workout tracking is up to 18 hours. Off-grid, satellite can reach emergency services or a contact when there is no cell tower - that path does not go through Merge, and it does not need an iPhone in your pack. MIL-STD-810H, IP6X, and 100-meter water resistance are the same class of hardware independence as earlier Ultras. What Merge adds after that first iPhone activation is the Android phone: notifications that last as long as the 50-hour battery, health data that lands in Google Fit instead of sitting on the watch, and an internet link that keeps working when Ultra 4 and the phone are hours of trail apart.
