Apple Watch Ultra 4 and Garmin Fenix 9 Pro Both Stay Within 2 BPM of Chest Monitor in TechRadar Test

The test was conducted by TechRadar's Matt, who wore the Apple Watch Ultra 4 and Garmin Fenix 9 Pro at the same time, one on each wrist. For a benchmark, he wore the Frontier X2, an ECG-capable electrical heart rate monitor, on his chest. TechRadar said the route was more challenging than usual, with a long incline at the midpoint that made the tester's heart rate spike.

According to TechRadar, average heart rate was the figure of greatest interest. The publication noted that different companies use different processing algorithms, so heart rate data points will not match one-to-one. The useful comparison is whether a wrist-based LED wearable tells the same general story as a chest-mounted electrical monitor, which TechRadar said is generally more reliable than LED-based sensors.

TechRadar applies its own interpretation to accuracy margins. It classifies a difference of under 5 bpm as an insignificant margin of error, enough to keep using and recommending a device. A difference of under 10 bpm is generally fine for light or occasional exercisers who are looking at general trends, according to the publication, but not for fitness enthusiasts who care about heart rate zones.

In this test, the Garmin Fenix 9 Pro measured an average heart rate of 159 bpm, while the Apple Watch Ultra 4 measured 160 bpm. The Frontier X2 measured 158 bpm. TechRadar reported that all three devices were within 2 bpm of each other on average. The publication said the result showed the two watches were telling the same story about the tester's body during the 30-minute exercise session, aside from algorithmic processing differences.

The watches also produced similar estimates for other metrics. TechRadar said calorie counts, which can vary widely between devices, were close: both watches estimated a burn in the high 300s, at 388 and 375. The Frontier X2 also estimated a calorie count that was very different from the watches, but TechRadar discounted that comparison because the watches collect more information to draw from. The publication said it trusted only the Frontier X2's heart rate numbers.

TechRadar said it was more than happy with the ratings from the two watches and can continue to recommend them as extremely accurate health and fitness tracking tools. The publication also compared the devices beyond accuracy, noting that both are aimed at serious sports and endurance use and both include dive modes and satellite communication features.

Even so, TechRadar said the watches are not made equally. The Apple Watch's software, third-party apps and smartwatch functionalities far outshine the Garmin Fenix 9 Pro, according to the publication. The Garmin watch has a longer-lasting battery, rated at 10 days versus Apple's 48 hours, and includes more survival tools, such as an LED flashlight.

For buyers, TechRadar's recommendation depends on use. A multi-day adventurer should opt for the Garmin every time, the publication said, while the Apple Watch is nicer to use for day-to-day wear and shorter excursions, even though it will need a charge every other day.