At Yale’s main library, we have security measures in place where security staff checks to be sure that library materials are charged out to readers before they leave the building. They do this by looking at the due date slip for each book, matching the barcodes of the slip along with the book. We created a ‘home-grown’ system of electronically checking due dates as materials leave the building. The program gives out visual cues (similar to the red/green traffic light system) alerting the guard whether an item can leave the building or not.