A "re-lock" mechanism on a vault door will prevent the bolt mechanism from operating under which condition?

The re-lock mechanism on a vault door is specifically designed to enhance security by preventing unauthorized access during certain critical situations. The correct answer indicates that the mechanism will engage if there is an attack on the door or the combination lock. This feature acts as a protective measure; when tampering is detected, the re-lock mechanism ensures that the bolts cannot be disengaged, effectively locking the door down and preventing access even if attempts are made to override the locking system.

In the context of vault security, this is crucial because it adds an extra layer of protection during potential intrusion attempts. It serves as a deterrent and can delay or impede unauthorized access, allowing more time for security measures to respond to a breach.

The other options do not represent conditions under which a re-lock mechanism typically activates. A timer might control access based on scheduled intervals, a switch being flipped could refer to internal controls but doesn't inherently indicate an attack, and remote locking usually allows for operational flexibility rather than invoking security measures like re-locking under duress. Thus, the focus on preventing access during an attack highlights the purpose of the re-lock mechanism in maintaining the integrity of vault security systems.