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Well, that works to an extent. But there's two flaws.

First, by asking loud enough to be heard through a door, you're waking up anyone trying to sleep if the knocking/bell didn't.

Second, and more importantly, what they say doesn't matter. If it's a stranger (and it would be, anyone that knows me has my phone number and knows to get in touch first at that time of night), there's a zero trust situation. You hope things are legit, but you can never assume they're telling the truth.

Like, if I'm going to try to rob or fuck someone up, it isn't like I'm going to declare that when they ask who it is.

Why would I assume that the random stranger in the night is going to be truthful? I don't, I assume that any of the wide range of possibilities is in play, and prepare for them as best I can.

My default is polite but wary. Wary means prepared to handle a bad situation. It's just that simple.