One of my contributors, subnetD, brought this to my attention:
APC, yes the guys you know for backup power, has an access control system for racks that uses proximity cards for access. The controller itself, on the rack, offers web browser access – meaning you could find out remotely that your server room had been penetrated. You can set up access by user, card and time, for granular controls, and the logging features let you look at exactly who, exactly when.
If I were investing in one of these I’d add a web camera, because I don’t want to have to make a frantic drive to see who just tore my rack open. Read more: http://www.apc.com/products/family/index.cfm?id=347.