Locking and unlocking the vehicle using the keyLocking and unlocking the vehicle using the 
key  - Central locking system - Doors and windows - Controls - Audi S5 Owner's Manual - Audi S5

If the central locking system should fail to work, you can still lock and unlock the driver's door by turning the emergency key or spare key in the lock.

Fig. 38 Lock on driver's door
Fig. 38 Lock on driver's door

Unlocking

Ц Turn the key to position A to unlock the vehicle.

Locking

Ц Turn the key once to position B ⇒ Ц If you turn the key to position B a second time within 2 to lock the vehicle.
Ц If you turn the key to position B a second time within 2 seconds, this will lock the vehicle without activating the deadlock mechanism.

In order to switch off the anti-theft alarm*, you must switch on the ignition within 15 seconds after opening the driver's door. Otherwise the alarm will be triggered.

WARNING
Do not leave anyone (especially children) in the car if it is locked from the outside and the deadlock mechanism is activated: the doors and windows cannot then be opened from the inside.
Locked doors could delay assistance in an emergency, potentially putting lives at risk.

Note
Х The central locking switch and the release button for the boot lid
ignition is switched on. will function after the ignition is switched on.
Х If the vehicle is locked with the key when the central locking system is operational, it is only possible to unlock all the doors and the boot lid centrally with the key within the next 45 seconds. After this period, the key will only unlock the driver's door.