Hey man. I think you know the answer already - there is no way to make sure about it. It's the same questions as "How can I make sure that my software is not hackable". But are you going to live without any digital devices, probably not. Change your router password periodically, unplug devices when you don't use them, put tapes on cameras or deactivate them if not needed...I hope we can all own our own privacy. Unfortunately, it's impossible if you want to live in the modern society.