The key still works from the other side when the lock is installed, as the Smart Lock PRO (5th Gen) CH cylinder is compatible with existing cylinders that have an emergency and danger function, allowing manual key operation from the outside even when the smart lock is installed on the inside.

However, compatibility issues can arise with certain knob cylinders (e.g., KABA or KESO rotary knob systems), where adapters may be required or the key function may be limited or not work properly without changing the cylinder. For standard Euro profile cylinders with emergency and danger function, the key remains usable from the outside side.