Amazfit T-Rex 3 (48 mm) / Samsung Galaxy Watch5 (40 mm, Bluetooth)

There is also a night display mode.

Sapphire crystal is a glass material that strongly resists scratching. The 44 mm version has a 1.4-inch, 450 × 450 screen.

The 22 mm strap is a standard width and can be swapped.

10 ATM means withstanding the pressure of 100 metres of still water for up to 10 minutes. Breath-hold training and testing are downloaded through the Zepp app.

A full charge takes about 3 hours; a magnetic charging base is in the box but no USB-C cable. Low-temperature mode gives 28 hours with GPS on and 32 days with it off. The maximum GPS mode works only in hiking and climbing modes.

Dual-band positioning receives two frequencies from the satellites to reduce drift from reflected signals among tall buildings and dense trees; it uses more battery. Automatic mode switches settings based on signal strength.

The watch offers an altitude assistant, storm alerts, compass, sunrise/sunset and tide information, and prompts for blood-oxygen readings at high altitude.

The electrical heart signal is used for ECG and bioelectrical impedance for body composition estimates; availability of these features varies by country.

Wi-Fi is used to download software updates without the phone. The watch shows incoming calls but cannot take Bluetooth calls; quick reply works on Android only.

This version has no LTE; the LTE version is sold separately.

Chest straps, running/cycling power meters and cycling speed/cadence sensors can be paired; data can be exported to apps such as Strava, komoot and Apple Health.

WPC is the body behind the Qi wireless charging standard. The 44 mm version has a 410 mAh battery.

The watch works with phones running Android 8.0 or later with more than 1.5 GB of RAM; it cannot be used with an iPhone.

5ATM suits shallow-water activities such as swimming, not diving.