I have to say that I have been somewhat amused by some of the posts on this thread. As far as I know all modern cars with central locking allow for the doors to be opened from the inside when locked outside. I would guess that it may well part of the construction and use reg's that this is the case to allow people to get out of the car in the case of an emergency. Certainly both our tintops work this way.
My Plus Four locks both doors on one press of the button on the remote. Both doors can be opened from the inside. There is no "double blip".
Both doors unlock on one press too.
The key locks both doors and both can then be opened from the inside. However if you unlock with the key the driver's door unlocks whilst the passenger door remains locked.
Many modern cars have a deadbolt function which is activated by hitting lock twice on the fob. The first locks the doors where you can still unlock it from the inside but a double press of the lock button deadbolts the doors where one can't get out. IIRC a warning message about this is flashed up in some cars. The double lock on others disables the interior motion sensor so there is some truth around hitting lock twice for other functions.
