T-Rex Pro Review: Design and hardware Starting things off, we’ll need to note that like its predecessor and all of the company’s other smartwatch/fitness tracker offerings, the T-Rex Pro relies on RTOS for its software. RTOS stands for Real-Time Operating System and acts as an extension of your smartphone instead of something that can operate independently. Notifications are mirrored, meaning that your wrist will buzz every time that your phone does, but you won’t be able to reply to those messages or answer phone calls from your wrist. Those with anxiety about notification overload might want to look elsewhere, but on this front, the T-Rex Pro does a superb job. It would be nice to be able to message a quick reply back every now and then, but it’s not a make or break situation here. Instead, Amazfit has positioned the T-Rex Pro as a sort of G-Shock smartwatch without the worry of a steep price tag.