Abstract: There is described an indicator device for indicating the passage of time, the indicator device comprising an indicator section and a barrier section adjacent thereto, said indicator section comprising: an indicator material; a substrate material; and a first adhesive layer; the indicator material and the substrate material being in the form of one or more layers; the indicator material displaying different visible properties in response to the presence or absence of a chemical agent and/or the concentration thereof; the barrier section comprising a removable barrier layer, the removable barrier layer being substantially impermeable to the chemical agent; wherein on removal of the removable barrier layer, the concentration of the chemical agent in the indicator section changes over time, effecting a visible change. The device may be used to detect the presence/absence of oxygen, water, carbon dioxide, an amine, ammonia, and/or carboxylic acids or to indicate the passage of time.

Abstract: There is described an indicator device for detecting a change in atmospheric conditions, the indicator device comprising an indicator section and a barrier section adjacent thereto, said indicator section comprising: an indicator material; a substrate material; and a first adhesive layer; the indicator material and the substrate material being incorporated into one or more layers; wherein the indicator material displays different visible properties in different atmospheric conditions, and wherein the barrier section provides a semi-permeable seal configured to allow controlled flow to the indicator of an atmospheric agent that effects a change in visible properties of the indicator material. There is also described a method for preparing an indicator device, and products derived therefrom. The indicator device may be used to detect oxygen, water, carbon dioxide, an amine and/or ammonia, or to indicate the passage of time.