Not come across these new fangled deadlocks before then Paul???
Breaking a window and climbing out is the only way you'd get out I'm afraid.
When I go in to pay for petrol etc, the missus locks the car from the button inside, that way no one can get in, but they can get out if they need to. You can unlock it when you come back with the key button as normal.
E92fan - I'm sure pressing the dashboard unlock button twice won't work as any thief could break a window, reach in and press the button and get in - defeating the whole point of deadlocking.
BTW: pressing the lock button on your keyfob twice still deadlocks the car but disables the motion sensors so you can leave pets inside without them setting off the alarm (or wife and kids if you like!)