Fire heat detector and/or burglar alarm

A detecting device comprising a thermally conductive container having an open end, a resilient diaphragm mounted across the open end to close the container and for expansion in response to pressure changes in the container corresponding to variation of temperature externally of the container, said diaphragm having an outer peripheral portion in close-fit non-hermetic sealing engagement with the peripheral surface of the container at its open end to form an annular venting passageway between said surface and the peripheral portion of the diaphragm, the open end of the container terminating in a circumferential rim which is provided with an annular protruding lip for engagement with said outer peripheral portion of the diaphragm, and indicating means responsive to expanding movements of said diaphragm for translating the movements into audible sound, said indicating means comprising a conductive plate member mounted for actuation by expanding movements of said diaphragm, a buzzer connected at one end to said conductive plate and at another end to an electrical power supply mounted vicinal to said container and said buzzer, and a switch for connecting said conductive plate to the electrical power supply to actuate the buzzer.