Apple Watch SE GPS with cellular support + fall detection

Hi,

If I have a Apple Watch SE GPS with cellular support, but I don't have an Iphone, can I still use

the fall detection feature with sending an SOS message to pre defined contacts?

I want to buy the watch to my grandma and she doesn't have an Iphone , I basically want to get an SMS or a all in cases she falls and i'm wondering whether I also need to buy an Iphone or does the watch itself with cellular will be enough...

Thanks,

Niki