Although there is generally no internal border control in Schengen Area, it can be temporarily reintroduced. The page lists current border control reintroduction as well as historical data.<p>Degrees vary. For example, some kind of Germany's border control with Austria started as early as 2015 and is still active to this day. I've seen it in a train from Salzburg to Munich in 2019, but it was like a routine ticket inspection. Just the German police checking passports and visas instead of DB officers checking tickets.