Hopefully cellphones weren't allowed? Otherwise it would be interesting to hack the phone to go to "record AM signals" if there's no cell/wifi/FM/GPS signals (if it were on a plane it would still see GPS signals). Or maybe to announce its presence using ultrasonic, so if there's also compromised machines/CPUs/hypervisor environments inside the secured environment, it would detect the "Hello" and start uploading data to it. Later when the phone user reconnects to the cell network, it can upload your secret data..
Of course they were forbidden, as it was every not authorized device. The physical security was tight. I just entered it during the building, before the certification (I was in a manager role in the building)
