You say you have a passport for the schengen area. I take it this means you are a citizen of an EU or schengen country and that country issued that passport? If so, there is no visa. You cannot overstay as an EU citizen as you can live in any EU country (single europe act 1986, came into effect 1992, supplemented by the Schengen agreement in force 1995). Technically if you're in a country for more than 3 or 6 months (depends on the country) you're supposed to register as a resident, but as you say with no border checks they don't know how long you've been there. Even non schengen countries (UK Ireland Bulgaria Romania (Cyprus?)) you don't need a visa, just show your passport. However they will know how long you've been there. Not a lot they can do if you overstay as you have EU right to be there. If they deport you, you can re-enter immediately.
I wouldn't worry about it.