The deadlocks message means under no circumstances leave your key in the ignition, and get out and shut the door. If you do I will deadlock the doors on you and then you will be in bother. Especially if you have the 2 keys on the key ring.
When I questioned the dealer about it when I had the Superb, he advised me it’s to warn you that the doors will be deadlocked when you lock them… In case you have kids in the car.
Though no car ive had has beeped and bonged with some form of warning than my Hyundai. Must be a Korean thing!