I didn't know anything about this (because I've never owned an Apple Watch) so I searched it:
https://support.apple.com/en-us/HT208944
Apple doesn't say anything about an added charges, so I don't think there are any, unless the ambulance shows up for a false alarm, then maybe you'd be on the hook for some fees, maybe not.
https://support.apple.com/en-us/HT208944
Apple doesn't say anything about an added charges, so I don't think there are any, unless the ambulance shows up for a false alarm, then maybe you'd be on the hook for some fees, maybe not.