A container assembly with an expiration date alarm that preserves its battery life by only triggering its alarm when needed. The container assembly includes a container for enclosing a food item, medication, or other product that should not be used after an expiration date; a sensor for sensing when the container has been opened; an alarm; and a timing circuit coupled with the sensor and the alarm for triggering the alarm only if the container is opened after the expiration date has been reached.