Most apartments and even with rental homes the owner / manager has to give you a 24 hour notice before they can show up and or enter your home / apartment. this all depends on your state But thats how it is here in California. Also to add if you live in a state like mine and im sure others in California can agree to this, WE really dont talk to our neighbors much. I have lived in the same home for 10 years and have never talked to the people across the street other then a "hello" and "hi, how are you?"
a good carbon filter and a game plan is a must, but start out small and work your way up. look at your utility bills each month and go from there.