What is the MOST effective method to prevent tailgating (unauthorized entry following an authorized person) at a data center entrance?

The most effective method to prevent tailgating at a data center entrance is the use of a mantrap or security turnstile system with individual authentication. A mantrap is a physical access control system consisting of two interlocking doors. An individual enters the first door, which then closes and locks before the second door can be opened. This prevents anyone from following closely behind an authorized person. Access is granted only after the individual inside the mantrap has been authenticated using a method like biometric scanning, smart card, or PIN code. Security turnstiles, especially those with height and anti-tailgating sensors, provide a similar level of protection. These turnstiles allow only one person to pass at a time and use sensors to detect if someone is attempting to follow closely behind an authorized person. If tailgating is detected, the turnstile will lock and an alarm will be triggered. These systems physically enforce single-person entry, making it extremely difficult for unauthorized individuals to gain access by following an authorized person. While security awareness training and policies can help to discourage tailgating, they are not as effective as physical barriers that prevent it from happening in the first place.