In many threads about leaving children alone at x age, people say they would leave them alone but not let them answer the door (though others say they'd not let them use the oven and make them have a takeaway, which presumably would need answering the door...)
I don't get why answering the door is a problem. Mine have since age 5 or so, when we stopped bolting it to stop toddlers escaping. In all the years I've lived here, people ringing the bell are daily posties and couriers, who hand over a parcel or wait for an adult to get down to sign, or child says mummy is having a nap, please leave it next door.
Then there's a few neighbours wanting to borrow tools/ask if I can take their kid to school. A few chuggers. The police, a couple times asking about the house opposite. 15 years of a slightly-dodgy area and never any problem.
So now ds is old enough to stay alone for a bit (max half an hour), I've told him to put the chain on before opening the door, and only take it off if he knows who it is, and if he's worried it would be OK to slam the door shut.
What do others do?