I live in an area where leaving doors unlocked overnight or even whilst you pop to the shops is no big thing. I can even leave my car unlocked overnight. But things changed recently as there have been a spate of car thefts where the thieves have entered the open house, taken the car keys, done whatever they do with it and returned it quite often with the fuel topped up.

The only reason this was noticed was because sometimes it wasn't returned to the exact same spot or the mileage increase was spotted.