Abstract: A device for indicating the current pressure state within a closed container, the device having at least a first substrate having a first set of displacement abilities; at least a second substrate having a second set of displacement abilities different from the displacement abilities of the first substrate; wherein the first and second substrates are held in separable abutment and displacement of one of the first and second substrates causes separation from such abutment producing an indication of either vacuum or pressure within the container. Also included is a method for indicating a pressure differential between the pressure in the interior of a closed container and the ambient pressure that includes deploying a pressure differential indicator on the container such that a first side is exposed to the interior of the container and a second side is exposed to the ambient pressure; and creating a pressure differential within the container.