NCIDQ IDFX Practice Exam

A glass break detector uses which method to identify a break?

1. Vibrational sensing or metallic foil

2. Infrared beams

3. Magnetic contacts

4. Photoelectric cells

The correct answer is: Vibrational sensing or metallic foil

A glass break detector primarily utilizes vibrational sensing or metallic foil to identify a break in glass. This method works by sensing the specific frequencies and vibrations that are generated when glass is shattered. The vibrational sensor is designed to recognize the distinct sound patterns produced during a break, allowing it to differentiate between the sound of breaking glass and other ambient noises. Metallic foil can also be part of the detection mechanism; it may consist of a thin strip that, when broken or stressed from the vibration of shattering glass, completes or interrupts an electrical circuit, triggering the alarm. This method is particularly effective for large areas of glass, such as windows in commercial spaces, where a break could indicate a security breach. Other options like infrared beams typically function through motion detection, where a beam is broken by an object passing through it, making it less suitable for detecting glass breakage specifically. Magnetic contacts are used in door and window sensors to detect whether these points are open or closed, but they do not address the characteristics of glass breakage. Photoelectric cells, while useful for detecting light levels or presence, do not relate directly to the mechanics of glass shattering. Therefore, vibrational sensing or metallic foil remains the most relevant method for a glass break detector.