Assuming there are no people registered in your Home assistant that would enter the shopping area, the trigger could simply be a state condition for the zone state to change not_to 0. If you have multiple,zones you want to test, then you can create triggers for each, and fill the trigger id with the name of the zone you are looking for.
I’m not that good in looping over persons with a state equal to that specific zone, so maybe someone else can answer that. If there are persons in HA who are not doing the shopping, you could probably filter them out here too. However, there’s also the problem of selecting the right notifier for each person.
So maybe one automation per person to check then entering the zones you need would not be such a bad idea. Also because that automation can easily be disabled if the person does not want to het the notifications for a while.