@TechConnectify
Love this.
It's funny, I live in an old mill, and the old fire doors are still hung up for decoration.
They're basically big doors that sit on a diagonal rail with a release mechanism. In the event of a fire, somebody fleeing is supposed to knock it off the catch, causing it to roll into place in front of the doorway
@aer
If properly installed, they are also self-closing in case of fire.
They have a cable or chain holding the door open, with a fusible section that melts when there's a fire nearby.