Abstract: A door, such as a fire door or a security gate, for blocking a throughway or opening in an exterior or interior wall of a building, such as a doorway or countertop window, has an open position and a closed position. A force, such as gravity, a counter weight or a spring, tends to move the door toward its closed position. In the case of the fire door, a disengageable stop holds the door in its open position. The disengageable stop includes a brake actuator for releasing a brake. An expandable linkage, having a normal length and having an elongate length when an external force is applied thereto, has a first end connected to the brake actuator. A second end of the expandable linkage is connected to a fire condition sensitive device, which releases the second end upon a fire indicative condition. With the fire door, or any other type of door, a DC generator is connected to the door and produces power as the door moves from its open position to its closed position.