This paper describes various sensors operating on tile principle of solid state ionics that sie being developed at Radiochemistry Laboratory of IGCAR. High temperature electrochemical meters for monitoring trace levels of hydrogen, carbon and oxygen in liquid sodium coolant circuits of fast breeder reactor have been developed. Sensors for measuring hydrogen and oxygen concentrations (in trace as well as percentage levels) in gas streams and ambients are in advanced state of development. A semiconductor based sensor for measuring trace levels of hydrogen sulphide in air, needed for surveillance of ambient safety, has been developed.