Abstract: An apparatus for signalling an operating condition of a cooking vessel is provided to signal a user of the cooking vessel when a preset condition is reached in the cooking vessel, e.g. temperature or pressure. Cooking vessels are frequently provided with an operating condition display device, such as a thermometer or a pressure gauge, which have a measurement scale and an indicator element moving relative to the measurement scale to indicate the internal condition of the cooking vessel. The apparatus of the present invention provides a housing having therein a detector for detecting a change in the reflected surface light from the operating condition display device caused by the presence of the indicator element of the display device. When the detector detects the change in the reflected light due to the presence of the indicator element, a signalling device, such as an acoustical or optical signalling device, is activated to signal the user of the cooking vessel.