Well that was freaky

[Gemini Cricket]

Frodo will bark at the sounds he hears throughout the house. The dogs may be conditioned to bark at the door opening. If the wind blew open the door, they might be reacting to the sound of the door opening. However, when there's someone at the door and Frodo sees him/her, his bark is vastly different. It is more intense and evil sounding. Do your dogs have a different bark when they see someone? Was that kind of bark you heard? It may be a clue.

Also, do you usually keep the bottom door lock locked? Or do you rely totally on the latch at the top? I'd get into the habit of locking the door with the lock on the knob if you have one. If it was locked, then someone jimmied the door open. Is there evidence of that anywhere?

I'd also invest in an automatic sensor that turns on the light when someone is at the front door.

My 2 cents.