Great idea for a thread 
I agree! Although I think something similar exists already (tho not quite the same) I don’t remember the name of the app but a friend and I were driving somewhere once and his dad called him and I heard him say “are you coming here then?” after his call ended I asked whether he might have saw us in the car somewhere or something - he said all of the family are on an app where you can keep an eye on each other’s location 
I guess it updates location while running in the background 
Not the kind of app I’d want to install tbh! So your gran’s idea is much better! 
I’d like someone to create a spam filter app that actually works, and one that auto-skips YouTube ads!! 