Analog fire sensor

An analog fire detecting system in which a plurality of sensors produce analog data corresponding to a physical state such as temperature, smoke density, etc. relevant to a fire condition. The values of such analog data are compared with a predetermined threshold level, and if the threshold level is exceeded the analog data is transmitted to a central station in response to a polling signal therefrom. A CPU in the central station determines, from the analog data from the sensors, if there is a possibility of a fire and if so makes a predictive calculation of the remaining time until a fire condition will be reached. An alarm is given when such predicted time falls below a preset interval.