Abstract: A battery-powered gas detector comprises a gas sensor coupled to a current source and a power supply. The power supply generates a relatively high voltage when the gas sensor is warming up and a relatively low voltage after the sensor has warmed up. The gas sensor, which is responsive to the presence of a gas, is coupled to an amplifier having a variable sensitivity circuit. The amplifier is connected to a microprocessor that determines the concentration of the sensed gas and provides a visual indication of the concentration on a display. The gas detector can sense the presence of a variety of different gases. The gas concentration of the sensed gas is determined based upon the magnitudes of a gas sensing signal generated by the amplifier, a calibration signal generated during a calibration routine when the detector is in a controlled environment, and an error signal generated when the detector is in a no-gas environment.