Sputtered films of CuBr with inter-digitated copper electrodes are used as electrochemical detectors for NH, gas. The current-voltage characteristics are ohmic and depend on the NH, partial pressure, P, with a fast response. The quantitative relation between the resistivity change Delta rho and P is described by a Langmuir-type adsorption isotherm with an adsorption constant K = 12 mbar(-1). The square-root time dependence of rho is consistent with a diffusion-limited aging mechanism.