2A is a general-purpose type gas sensor which has a wider range of application; it is mainly used for alarm. 3A refers to the model of general-purpose LP gas sensor.

Low-power catalytic combustion gas sensor, which is mainly used in combustible gas alarm and portable gas leak detector.

NAP-50A is catalytic combustion gas sensor, which is characterized by small size, low-power, and high-speed response. The detectable gases include methane, propane, hydrogen, hydrocarbon, and etc. Moreover, NAP-50A also has extremely low sensitivity to alcohol and anti-false alarm function.

NAP-56A is a small-size, low-power catalytic combustion gas sensor, which is the improved version of NAP-55A, and its sensitivity has been improved 15% compared with NAP-55A. Its shell and base are made from corrosion-resistant, high temperature resistant metal and bakelite, and it enjoys much longer service-life and mainly used in combustible gas alarm and portable gas leak detectors.