The Series 5 cellular WITHOUT a contract can still call emergency services
Series 5 Fall Detection and Emergency Services on Cellular Apple Watch Series 5 with no cellular contract.
Need to be 18 years or older.
Automatically offered to 65 or older.
https://support.apple.com/HT206983
https://www.apple.com/watchos/feature-availability/#branded-international-emergency
https://support.apple.com/HT208944
A GPS only model can piggy back off of the iPhone if it is nearby
You will need an iPhone 6s, SE (1 or 2), 7 or newer, running iOS 13 or newer.
The GPS only Apple Watch can do Everything the cellular model can do as long as your iPhone is nearby, where nearby is somewhere in the same 3-4 bedroom home (assuming typical wood frame construction). And of course when the iPhone is with you when you leave the house.
https://support.apple.com/en-us/HT205547