Abstract: A tamper-indicating device which is attached by adhesives to a closure and which includes a sheet of material, sensitive to an ambient condition such as light or oxygen, that effects a time-delayed, irreversible change in appearance in response to exposure to the condition, which is automatically exposed upon the opening of a closure, such as the removal of a bottle cap from a bottle. The device consists of a lower sheet impermeable to the ambient condition and shaped to be attached at an underside to a lower closure member, an intermediate sheet superposed to the lower sheet and including the sensitive material, and an upper sheet, impermeable to the ambient condition, and superposed to the intermediate sheet and shaped to be attached to an upper closure member. A first, relatively strong adhesive which is used to attach the lower sheet to the lower closure member and to the intermediate sheet, and to attach the upper sheet to the upper closure member.