This paper describes an inexpensive point sensor for chemical detection. The sensor is based on a novel integrated optic interferometer that provides a highly stable platform for measuring low concentrations of specific chemicals in gaseous or aqueous environments. Sensing is accomplished by monitoring refractive index changes in a thin-film surface coating, with specificity for a particular chemical achieved by using a surface coating that selectively interacts with that chemical. Multiple surface coatings can be used for simultaneous detection of several chemicals. This approach has a number of key advantages: (1) it is capable of quantifying concentrations down to at least the parts-per-billion level, yet has a broad dynamic range, (2) it is rapid response (<EQ 1 second), allowing real-time detection, (3) it is fully reversible, permitting continuous measurement, (4) it neither generates nor is susceptible to environmental interference (e.g.; electromagnetic fields, radiation, corrosive chemicals), (5) it is compact (centimeter dimensions), (6) it requires minimal power (<EQ 100 milliWatts), and (7) it is low cost. Chemicals investigated to date include ammonia, benzene, toluene, chlorine, chlorine dioxide and hydrogen. Applications range from worksite and workforce monitoring to agricultural and industrial process control.