A warning device

A thermal warning device for a door comprises a thermochromic indicator adapted to display a warning when the temperature at the surface of the door exceed a predetermined level indicative of fire. The thermochromic indicator warns of the presence of fire by changing colour and/or by displaying a warning message or symbol. The thermochormic layer may be formed using a thermochromatic ink, in particular a luminescent thermochromatic ink. A thermal link, e.g. a metal pin, may be provided to transmit heat to the thermochromic indicator from the side of the door opposite to the side to which the device is fixed. The device may include two thermochromic indicators adapted to be fixed to either side of door and connected by a deformable thermally conductive strip which can be bent around the edge of the door.