Lord Ba'al
Well Known GateFan
All it takes is the right key, baby.
Seriously though, I'm not sure what you're describing as a "deadbolt". How do you people lock your doors from the outside if not with a keyed deadbolt?
They are mainly intended as extra locks for when you're inside and sleeping. Some of them have a double function of enabling a door or window to be placed at a tiny crack open while still being "locked". That last part is of course not to prevent burglars from entering but more to make sure the wind doesn't bash the thing around.