The use of hydrogen as a tracer gas has also generated much interest due to helium supply issues. Two hydrogen sensor technologies are currently in use in production leak testing applications. The first is the same magnetic sector mass spectrometer technology that is used in helium leak detectors. In most commercially available helium mass spectrometer leak detectors the option is available to tune the mass spectrometer to detect hydrogen. The second detector that has gained some popularity is a chemical sensor that is specific to hydrogen gas and is typically mounted on the end of a handheld probe for sniffing applications.