I guess I was assuming that the OP had a cell phone. I have one, but where I go there is often no signal.
There are cell phones heavily advertised to seniors (Great Call is one) and I think that many of them have medical alert buttons. Don't know if those are the ones good in registered areas only.
No alert is any good if you don't have it on you when you need it: in a plastic zip bag in the shower with you, in your pocket, by your bed. And of course you have to be conscious in order to use it. Perhaps add some sort of daily check-in feature, automatic or otherwise, sort of "if you don't hear from me every day by X hour, call for help". Some of the satellite trackers have automatic map track features so your location would be known.
Try cell phone first (two-way voice). If that doesn't do it, add a more sophisticated system.
