Re: Files are not testimony
"Let a cop walk in your unlocked front door, and see what he finds walking through your house, without needing a warrant..."
The officer would still need permission to enter your house whether the door was unlocked or wide open. They will ask if they can come in and if you give them permission, you change the scenario a lot. If they can see what appears to be criminal activity in the house from your open front door, that may also give them some leeway. If there is a coffee table piled high with a white powder, a scale and a pack of little zip lock bags in plain view, you're nicked.