Apple Watch cellular uses eSIM, so once I pair with iPhone with physical SIM the eSIM gets setup in the watch. You can then put the physical SIM in any device,

Apple Watch cellular uses eSIM, so once I pair with iPhone with physical SIM the eSIM gets setup in the watch. You can then put the physical SIM in any device, Apple Watch's cellular is independent. Apple Watch as AFib alerts, I've linked the health features in my blog.