If your lock cylinder has an emergency function, you can carry on locking with your old key. If you can still turn the key from the outside even if a key is in the lock on the inside, the lock has an emergency function. You can use the Nuki Smart Lock on locks without an emergency function (or priority function). However, we recommend to use the Smart Lock on locks with an emergency function only. You can have the emergency function retro-fitted to your existing door lock. For this, contact your locksmith.