Which of the following is the best way to secure an on-site data center against intrusion from an insider?

An access badge system is the best option for securing an on-site data center against insider intrusion because it provides granular control over who can enter specific areas and when. It creates an auditable log of entry and exit, allowing for accountability and forensic analysis if an incident occurs. While bollards protect against vehicle-based threats, they do not address human intrusion. Motion sensors detect presence but don't identify individuals or prevent unauthorized entry. Video surveillance records events but is a reactive measure for identifying intruders rather than a proactive control for preventing unauthorized access.