Element One, Inc. is developing novel indicators for hydrogen gas for applications as a complement toconventional electronic hydrogen sensors, or as a low-cost alternative in situations where an electronicsignal is not needed. The indicator consists of a thin film coating or a pigment of a transition metaloxide such as tungsten oxide or molybdenum oxide with a catalyst such as platinum or palladium. Theoxide is partially reduced in the presence of hydrogen in concentrations as low as 300 parts per millionand changes from transparent to a dark color. The color change is fast and easily seen from a distance.In air, the color change reverses quickly when the source of hydrogen gas is removed in the case oftungsten oxide or is nearly irreversible in the case of molybdenum oxide. A number of possibleimplementations have been successfully demonstrated in the laboratory including hydrogen indicatingpaints, tape, cautionary decals, and coatings for hydrogen storage tanks. These and otherimplementations may find use in vehicles, stationary appliances, piping, refueling stations and inclosed spaces such as maintenance and residential garages for hydrogen-fueled vehicles. The partiallyreduced transition metal oxide becomes semi conductive and increases its electrical conductivity byseveral orders of magnitude when exposed to hydrogen. The integration of this electrical resistancesensor with an RFID tag may extend the ability of these sensors to record and transmit a history of thepresence or absence of leaked hydrogen over long distances. Over long periods of exposure to theatmosphere, the indicator?s response may slow due to catalyst degradation. Our current emphasis is oncontrolling this degradation. The kinetics of the visual indicators is being investigated along with theirdurability in collaboration with the NASA Kennedy Space Center.KEYWORDS: Hydrogen, sensor, detector, visual indicator, thin film, coating, tungsten oxide,molybdenum oxide