Abstract: A temperature actuated keying device for use in an automatic door closing mechanism which comprises a pair of thin, long plates for clamping members pivotally connected to each other at overlapping ends thereof by a pin so that both plates can be opened or closed in the same plane relative to the pin as in scissors, a washer portion and a spring provided between the clamping members and a fuse plate consisting of a pair of component plates connected by a fusible material to each other to form the fuse plate which is removably mounted between the other ends of the clamping members. The keying device is attached to a door closing mechanism to hold the door open in normal condition, and to release the door to close in case of emergency when the fusible material melts to separate the fuse plate, thereby opening the keying device.