Apple Watch Series 4 Model A1978

I just purchased a new iWatch and my friend is saying it’s not cellular compatible because it doesn’t have the red circle on the side button. Mine is just black there is no outline of red does that mean it isn’t cellular compatible. I bought it for that reason. My friend is able to leave his phone anywhere but still access it via his watch because of the cellular compatibility. How do I know if my watch has that service.