I find my brain is a very good Random Thought Generator. Today's gem: back in the Paleolothic Age - or whatever - were there doorbells on yurt or cave entrances? My dogs have NEVER lived in any house with a doorbell, yet they wake right up and bark at the door when the sound of a doorbell emanates from the TV set. They do this with the sound of someone knocking on a door, too, but gosh, they have heard that sound in their lives, so I cannot attribute their responses to instinct or "genetic memory."
Or could this be ingrained in canine genetic memory with only a few generations of selective, domestic dog breeding?
My two dachshunds give me such injured looks when I shush them during their false Polite Intruder Alerts.

Since my 3 rotties barked at airplanes flying overhead, I"m wondering if anything out of the ordinary sets them off. Mine barked at the TV door bell too!