Abstract: A detecting apparatus includes a processing device connected to a sensor, a programmable memory device and an alarm device. The sensor generates a signal output that varies according to a detected condition. The processing device includes a converting unit for converting the signal output of the sensor into a digitized value, a memory programming unit for storing a reference value in the memory device, and a comparing unit for comparing the digitized value from the converting unit with the reference value in the memory device. When the processing device is operated in a calibrating mode while the sensor is placed in a standard environment, the programming unit stores the digitized value from the converting unit as the reference value in the memory device.