Earlier quoted context omitted.
Buy your kid a dumb watch, explain it to him, tell him to be home at 6, otherwise he will be grounded. Worked for ages, should work for now. (Or to be somewhat less snarky: We should not try to solve every problem with technology, just because we can.)
Technology solves a problem that the old ways could not, or they were inferior. I recall as a kid my parents driving to the park where we were because a family emergency meant we unexpectedly had to leave now - they would have preferred we walk home while they pack the car (the park was the opposite direction we had to go). I can say be home at 6, but it is easy to lose track of time. Or say 6 and then realize supper…
You have only a very limited number of grandparents that could suddenly die and need the kids to be home right now.
And why should the kids need to compensate for your problems with planning of the supper?
These were never really problems before, but now people start to force their tight schedules on kids by tracking them all around the clock. That's not okay.