Kimo has a wide variety of electrochemical interchangeable sensors.

O2 long life : 0-21 %
CO-H2 : 0-8,000 ppm
NO : 0-4,000 ppm and NO low range : 0-500 ppm
NO2 : 0-1,000 ppm
SO2 : 0-5,000 ppm
CH4 : 0-10,000 ppm