Yeah, push the handle which is the same as locking it normally from the outside (but not deadlocked). I've gotten into the habit of doing it when I get in the car now, even before starting the engine.
It doesn't deadlock it, if it did you wouldn't be able to get out even by pulling the handle. I suppose a determined carjacker could still smash your window and pull the handle.
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2005 Fiesta ST - wrote off
Newman fast road cams, Fusion Fabrications custom inlet manifold, custom exhaust