[owkaye]

> We did actually look at doing this for spouses -- not to detect cheating (a cheating spouse will be even more motivated to subvert the system than a child), but to help out with stuff like "are you near the supermarket? Can you pick up some milk?", but fundamentally people don't seem all that interested in it.

They just call each other in this situation which means there's no need for some additional program on a special phone that they may not even own.