There was a scam going around in which someone rings a doorbell in the wee hours of the morning. Stating someone robbed them or their car broke down. Something like that. They ask to use your phone, meanwhile others in the group come into your house and they keep you distracted as they rob you. A friend of mine unfortunately fell victim to this last year. If you answer the door, tell them that you are calling the police and do it. They will flee.
Has this happened more than once? Do you have a wireless doorbell? After I installed one I bought at Home Depot, my doorbell would ring but there’d be no one on my porch. I was perplexed for months until I noticed that every time this happened there was someone at the door on my neighbor’s porch across the street. Their wireless doorbell was apparently set to the same frequency so whenever someone pushed their doorbell, it rang at my house.
Same here with the wireless doorbell. We had to finally get rid of ours, after we realized it rang everytime there was someone at the door of the house across the street from us. Hope that is all it is for you. If not, I would be installing cameras.