Although some would consider a computer room equipped with the three high-tech security systems, meant to prevent any intrusion, as missing the "most basic security measure" of video surveillance, video surveillance is often not permitted in highly classified areas where there is a risk that unauthorized personnel - such as the security personnel - may see the material. The security personnel may theoretically be cleared for that classification but they would not have a "need to know" the information contained within AND video surveillance visible in another area would defy the measures taken to keep the information in a secure room.
However, a simple device to lock out the keyboard, of any other I/O devices or ports, when there was no authorised operator officially present, would be simple to implement, very efficient, and pose zero potential for information leakage.