A type of annunciator that uses an electrically vibrated clapper to repeatedly strike a gong is known as what?

The correct answer is the solenoid-operated bell. This type of annunciator functions by employing an electrically operated solenoid mechanism that generates rapid, repetitive movements. When the solenoid is energized, it causes a clapper to strike a gong, producing a ringing sound. This design effectively uses electromagnetic principles to create a distinct auditory alarm that can alert individuals to various events.

In the context of intrusion detection and alarm systems, solenoid-operated bells are valued for their reliability and durability, as they provide a clear, loud signal when triggered. Understanding how this system operates is crucial for those studying intrusion detection mechanisms, as it illustrates the principles of alarm activation and sound generation in security systems.