A method for alerting a user when an item is missing from a container. The method comprising implementing, by an item tracking system, a plurality of steps. The steps comprise determining an expected set of items for the container, using an item sensor associated with the container to determine a current set of items in the container, comparing the current set with the expected set to detect whether any of the expected items is missing from the container, determining a packing area for the container, tracking a location of the container, and causing an alert to be outputted via a user interface, in response to the container leaving the packing area with any of the expected items missing.