Amazfit T-Rex review

Internals

Before we get into activity and sleep tracking, and performance on the T-Rex, it is important to note what hardware is inside it. Since that will dictate what expectations we can have.

Actual hardware information on a chip level for Amazfit products is hard to come by. However, it is fairly apparent that wearables like the T-Rex, we are currently reviewing, and its Amazfit GTR, GTS and Bip siblings are closely-related in their functionality to other Huami devices. Notably, the all-popular Xiaomi Mi Band series.

The latter tend to be powered by custom, low-energy IoT circuits, courtesy of Dialog (SmartBond DA14580 in the original Mi Band and Dialog 14681 in the Mi Band 3). We bringing-up such specifics to contrast these "smart wearables" to other, more-versatile and powerful solutions that tent to appear in "smartwatches" and more feature-rich products. For instance, the Amazfit Verge is advertised as running on a 1.2Ghz dual-core chipset, of some sorts, with 512MB RAM and 4GB storage. This is just one of the defining aspects of a "smartwatch", as compared to a smart wearable. The other side of the story, of course, being the 5 day advertised battery life on the Amazfit Verge, as opposed to the over 20 day one on the T-Rex.

More isn't necessarily universally better in the smart wearable world, though. And in this regard, the T-Rex appears to strike a nice balance. Compared to its Amazfit GTR sibling, though, there are some notable downgrades. Instead of a 6-axis acceleration sensor, you get a 3-axis one. And the air pressure and capacity sensors of the GTR are missing, outright.

Still, the all-important PPG biological tracking optical sensor is there. It is dependable, as far as getting a consistent reading out of it is concerned. The accuracy of said reading, however, is often off. Some times it will measure an elevated heart rate while resting. Other times, it will consider a bike ride leisurely, with a sum 100 bpm measure. That's more of a critique towards optical heart rate measurement tech in general, though.

GPS performance on the T-Rex is a saving grace. Just like the Amazfit GRT, we keep circling back to as a good point of reference, the T-Rex has a dedicated GPS receiver. It's an A-GPS unit, as expected. So, you do need to frequently allow A-GPS data to be fetched from a connected phone for it to work properly. With that taken care of, the actual GPS performance of the T-Rex is stellar.

Tracking performance

Getting a location fix usually takes less than 30 seconds, and the T-Rex rarely loses its fix. Even when it does, which usually happens when entering a building or tunnel, it reacts almost instantly to the fact and then recovers the fix just as quickly. This is probably one of the few aspects in which it surpasses its Amazfit GTR sibling in performance.

The T-Rex website brags about this high level of GPS accuracy, quoting things like a powerful Sony GPS + GLONASS chip solution. However, the more likely explanation for this GPS boost over the GTR is probably a better body design and internal antenna solution. Even the simple fact that the bulk of the T-Rex's shell is plastic, as opposed to metal, could be making a difference.

If you are after optimal GPS performance, the T-Rex is notably the better of the two siblings. It also easily outperforms the older Amazfit Bip in this category.

Exercise tracking

Activity tracking is, hence, a bit of a mixed bag. Exercise types that are heavily dependent on heart rate data can result in inaccurate numbers. Though, the calorie calculation is typically mostly based around averages on a time basis. So those should be fine.

On the flip side, the stellar GPS performance makes running, walking, trekking, hiking very accurate in terms of distance and plotted paths. The T-Rex even gets elevation metrics mostly right. We can only assume that this applies to skiing as well.

Sleep tracking

Sleep tracking is very hard to verify or cross-reference in any meaningful way. Still, we can attest that the T-Rex mostly got the fall-asleep and wake-up times correctly. Huami has been hammering-out the kinks in these particular algorithms for a few years now, so we can only assume the stats are at least mostly trustworthy. Whether or not the actual sleep pattern data is of any practical use, though, is a whole other discussion.

Battery life

Despite its noticeably bigger footprint, the T-Rex has a smaller battery than the bigger (47mm) Amazfit GTR model. Only by 20mA or so, which is not significant in practice. Even so, it feels like Huami could have filled the T-Rex shell with a lot more battery. This would have addressed the disconnect between expected and actual weight, for its size.

In regards to battery life, the T-Rex is a true marathon runner. Just like its GTR sibling, it can easily get over 20 days of normal use on a single charge. Huami has a very precise definition of what its "normal" usage patterns is: 150 notifications per day, 30 screen activations, 5 minutes of screen-on operations a day, and 30 minutes of run tracking every other day.

We can confirm that 25 days are achievable in practice. Our usage pattern frequently saw an excess of 150 notifications. Typically, a longer walk or bike ride, every other day, instead of a 30 minute run.

Of course, your mileage will vary, but you can probably count on close to a month without charging. We didn't have time to validate the 66-day claim for the Battery saver mode. Judging by our GTR experience, we have no reason to doubt that claim either.

Charging the T-Rex is quite snappy. You can get a dead unit to full in around two hours. Charging is done via a magnetic base, with a couple of pogo pins. There is only one correct direction, and the magnets make sure you get it right. The design has its flaws and it can be disconnneted with an accidental bump. It is functional, though, and a lot more efficient than wireless charging.