One of the best rugged smartwatches I've tested uses GPT-4o for coaching and UI control

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ZDNET's key takeaways

The Amazfit T-Rex 3 is available now for just $280 in one size and one color.The watch has a long battery life, durable construction, a vibrant display, AI elements, and extensive health and wellness functionality.
There is no speaker for hands-free calls or headset-free audio, and the Zepp smartphone app is still overwhelming.

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I started testing Amazfit smartwatches in 2018 and have been quite happy with the Balance I purchased at the end of 2023 that was then upgraded to Zepp OS 3.5. In 2020, I rocked an Amazfit T-Rex and found that rugged line to fit my lifestyle and large wrists better than smaller Amazfit watches, so it has been great to have a new T-Rex 3 strapped to my wrist for the past three weeks.

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When I first heard about the opportunity to test this watch, I wasn't that excited because I thought it was just going to be a bulkier Balance without much appeal to me. It turns out that this watch is built for those of us with larger wrists. Given my preference for big watches like the Samsung Galaxy Watch Ultra and Apple Watch Ultra 2, it seemed like a good fit. There was even mention of expanded AI functionality and connectivity with external sensors, so I was intrigued.

Also: Why I wear this $220 smartwatch even after testing Garmin and Samsung watches

The large 1.5-inch 480x480 pixels resolution AMOLED Gorilla Glass display is brilliant with up to 2,000 nits of brightness, making watch faces with lots of complications easy to view and interact with. I love that Amazfit added the ability to enable night mode, which changes everything on the display to one color. While almost every other watch that supports this function uses red text, Amazfit lets you choose from red, orange, or green, so I've been enjoying the green light on this review unit.

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The large capacity 700 mAh battery is advertised as providing up to 180 hours of continuous GPS tracking in max battery life mode and 42 hours with accurate GPS mode. Of course, I never ran straight for 180 hours, but I did run with the most accurate GPS option and saw about 3% to 4% battery loss per hour, so the 42-hour estimate seems fairly accurate. In typical daily use with two to three short runs per week, sleeping with the watch, some notifications enabled, and viewing wellness data regularly, I only charged the watch once after the initial charge, and it lasted me three weeks.

GPS tracking is also spot on, with the Amazfit T-Rex 3 supporting dual-band GPS and six satellite systems. I used the T-Rex 3 for running, biking, walking, and hiking with other GPS sports watches to check accuracy. Many of my activities were in heavily wooded areas, with the T-Rex 3 acquiring a quick connection and tracking almost on the exact same line as my flagship Garmin watches.

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One shortfall in the new Samsung Galaxy Watch Ultra is its inability to connect to external sensors. That is not a problem here for the Amazfit T-Rex 3, which connected perfectly with my Coros HR monitor, Garmin chest strap, and Garmin speed/cadence sensors. The T-Rex 3 can also connect to GoPro action cameras, the Core body temperature sensor, and more.

It seems one stand out feature of flagship watches is the ability to support underwater sports, as seen by the Apple Watch Ultra and the Garmin Fenix 8. The Amazfit T-Rex 3 takes things even further, with various certifications that support freediving down to a depth of 45 meters. Sorry folks, I'm not going to be able to test out this capability.

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Advanced sports data, including running power, VO2 max, recovery time, training effect, and training load are all present on the T-Rex 3, which is a bit surprising given its $300 price. The sleep tracking is close to other watches and is used by the integrated Zepp Flow AI system and Zepp Coach system to tailor and update your training plan. 

Also: The best smartwatches you can buy: Expert tested

The Zepp smartphone application is used to present the data captured by the watch, and there is a lot of data shown on multiple pages. The Zepp app has evolved over the years, but it continues to offer an exhaustive amount of data that may seem intimidating at first. Take the time to set up the app to your preferences, and then let Zepp Flow and Coach streamline your experience with practical and actionable insights.

The free Zepp Flow utility is an accurate and reliable AI assistant that is especially useful on a watch like the T-Rex 3. I've been using it to ask health and fitness related questions about my performance and data that the watch collected, as it is faster to use Zepp Flow then go through the various menus. I also like it for jumping right into a workout. Zepp Flow was developed using OpenAI's GPT-4o and provides full control over your watch, so you don't need to know exactly where things are buried in the watch UI. The Amazfit T-Rex 3 also supports an offline voice assistant for some basic functions, but I did not find it that useful.

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The Zepp Coach AI chatbot is very functional and walks you through a series of questions to optimize a training plan to meet your goals and preferred approach to training, starting with options to create a running plan or a basic AI plan to improve cardio fitness. The watch then monitors your data to provide guidance to help you reduce risk of fatigue and injury. This appears on the watch and in the Zepp app as insights and even prompts to visit the Zepp Aura chatbot. Zepp Aura provides some excellent, detailed answers and guidance on various health and wellness questions.

You can also combine the T-Rex 3 with an Amazfit Helio Ring if you don't want to wear your watch to sleep. Unfortunately, the Helio Ring continues to underreport my sleeping heart rate by 10 bpm, so I've been wearing the T-Rex 3 for sleep tracking.

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I've also been using the voice memo option since I often have ideas when I run. The T-Rex 3 has a microphone for the voice assistant and voice memos, but there is no speaker for hands-free calls or audio responses. You can reply to messages from a connected Android phone with your voice, but you cannot initiate any messages.

There is a lot going on with the Amazfit T-Rex 3, but the battery life has been fantastic, the AI coach, insights, and Zepp Flow assistant have been useful, and there is a lot to like in a big watch available for just $300.

ZDNET's buying advice

With the T-Rex 3, Amazfit continues to impress thanks to a brilliant large display, durable materials, powerful sensors, and helpful insights powered by AI. Having a smartwatch that lasts for weeks rather than days is a breath of fresh air.

If you like big watches, spend time outdoors where you want some watch map guidance, and take time to customize your experience, then the T-Rex 3 may be a perfect option for your next adventure.