Crash Detection

The watch needs to be paired with an iPhone and if it is a cellular watch, and you have a cellular plan for the watch, the iPhone doesn't need to be with you. If you don't have your paired iPhone with you or you don't have a cellular connected Apple Watch, it won't be able to call anyone.

It depends on which Apple Watch you are referring to. Any brand new Apple Watch from Apple will come with WatchOS 9. For it to pair with an iPhone, you'd need an iPhone which can run at least iOS 16. That means, you'd have to have an iPhone 8 or newer.