When testing walk-through safety devices, an important check is to ensure they __________.

The correct choice emphasizes the importance of ensuring that walk-through safety devices operate only when doors are closed. This is crucial for maintaining safety standards in hoistway operations. If these devices can activate while the doors are open, it could lead to dangerous situations, such as unauthorized access into the hoistway or potential accidents when the elevator is in motion.

Walk-through safety devices are designed to prevent entry into the hoistway under unsafe conditions, ensuring that the elevator operation is inherently safe for users. Therefore, their functionality being restricted to the closed-door position is a critical safety measure that helps to protect both passengers and personnel working around the elevators.

In contrast, the other options suggest scenarios that would compromise safety. For instance, if these devices activate at any time, it could lead to unnecessary disruptions or unsafe conditions. Resetting them manually may not provide the immediate response needed in an emergency, and tamper-proof features, while beneficial, are not the primary function of ensuring that the activation is limited to when doors are securely closed. Thus, focusing on the operation of these devices during specific safety conditions is essential for upholding elevator safety protocols.