Electromechanical and electromagnetic locks are considered fail-safe if they:

Fail-safe locks are designed to unlock automatically when power is removed. This ensures people can exit during emergencies such as fire alarms or power outages. It is a critical safety requirement in most building codes.

A may be true for integrated systems but doesn’t define fail-safe.

B describes fail-secure, which keeps the door locked during power failure.

D (Tamper resistance) relates to durability, not fail-safe function.