A delayed egress lock must open immediately when:

A delayed egress lock is specifically designed to allow for controlled exiting from a building, primarily used in situations where security needs to be balanced with safety. One critical aspect of these locks is that they must open without delay in emergency situations, particularly when life safety is at risk.

When a fire alarm is activated, it signals an imminent danger that requires immediate evacuation to ensure the safety of individuals within the building. Therefore, the lock must release and allow individuals to exit promptly, minimizing the risk of injury or harm during an emergency evacuation. This function aligns with safety codes and regulations that govern egress and emergency exits.

In contrast, other scenarios such as inputting a code or activating a backup power source do not represent immediate threats to life that necessitate the urgent opening of the door. Also, while physically forcing the door open may indicate an emergency, it does not inherently trigger the lock's release mechanism, as it could lead to unauthorized access or security breaches. Thus, the instant unlocking of a delayed egress lock upon the activation of a fire alarm is crucial for ensuring public safety.