Seems you need cell reception for it to work right...

Quite, cell coverage needed - so that is an issue.

If after something more flexible I sometimes take one or other of these:

http://oceansignal.com/products/plb1/

https://www.ordnancesurvey.co.uk/shop/brands/brand-garmin/garmin-inreach-mini.html

The former a PLB, press button if in trouble; uses satellite network (one-off buy need to register)

The latter similar SOS function but with two-way satellite mail and texting (monthly contract, can be pricey)