The oscillatory behavior of unidirectionally coupled overdamped bistable systems was studied. It was found that for an oscillating coupled system, the inclusion of the subthreshold periodic target signal resulted in the mixing of two or more frequencies in nonlinear devices. The frequency mixing was shown by the power spectral density response. The subthreshold time-periodic target signal was capable of inducing oscillatory behavior. These oscillations are finding application in the detection of very weak target signals.