The Doorbell

This happened about a week ago and usually, things do not bother me at all since I investigate other places. This did. I was sitting on my couch and working on my computer. I was expecting a package to be delivered to the front door was open. My ring doorbell never went off during this time. I was half sitting facing the door so I could see the delivery person drive up. I saw an arm from the elbow down come from the side of the door. Like someone was hiding on the side. Which would have been the same side as my doorbell. Knock three times and slowly pull back. Once the arm came into focus I actually turned my whole body towards the door. It was an arm and looked dainty so I am guessing female. You do see me getting up and checking all around the house on the Ring. 
For the past few months, our doorbell has gone off and it does not alert our phones we hear the ring. Then you will hear knocking and people who are in the living room will answer the front door. No one is ever there. We have had paranormal happenings since I was seven and I am now 44 so this is not new. This one just bothered me way more than anything else.