Abstract: A vapor or gas detector (12) that forms an element of a vapor or gas detecting and alarm system (30). The detector in one of its embodiments is configured as a three-section dynamic junction (16) consisting of a resilient substrate (22) having a resonant mechanical element (18) attached to its back and an absorbate (20) to its front. When no toxic vapors or gases are present, the element (18) is under a no-strain, no deformation condition and emits a first frequency signal. When a toxic vapor or gas is present, the absorbate (20) absorbs the gas or vapor which causes the substrate (22) to deform and, in turn, causes the element (18) to deform and emit a second frequency signal. This second frequency signal is applied to the system (30) where the signal, through a series of electronic circuits is processed. The processed signal activates a lamp (44a) and an audible alarm (44a) indicating that the detected vapor or gas has exceeded a preselected toxicity level.