The ball catch mechanism consists of a spring-loaded ball that catches and holds the door closed. Ball catch doors are generally used indoors.

What is a spring catch used for?

a catch for an interior or cabinet door that has a bolt operated by a spring.

How do French doors stay closed?

The fixed door on many French doors is held closed by a pair of barrel bolts that sink into the top jamb and threshold of the doorway. Even if these are tight enough to prevent the fixed door from moving, burglars may be able to work a screwdriver through the gap between the doors and unlock these bolts.