Abstract: A device and system for determining the status of the contents of a container by measuring the period of time which has elapsed since the opening of the container. The present invention provides a flexible mechanism for enabling the user to determine the usability or efficacy of the contents of the container, since such contents typically experience a higher rate of degradation once the container has been opened. Furthermore, the manufacturer is able to provide information related to the expiration date of an unopened container at the time of manufacture, but cannot determine the time at which the container is opened, and hence the expiration date after opening.