NCIDQ IDFX Practice Exam

What is the purpose of photoelectric cells in intrusion detection systems?

1. To sense window breakage

2. To detect when a beam of light is interrupted

3. To monitor sound levels

4. To send alerts when doors open

The correct answer is: To detect when a beam of light is interrupted

The purpose of photoelectric cells in intrusion detection systems is to detect when a beam of light is interrupted. These cells work by emitting a light beam, usually infrared, and monitoring its status. When an intruder crosses the path of the beam, it interrupts the light signal, which triggers an alarm or alert system. This method is commonly utilized in security systems as it provides a non-contact means of detection and can be effective over varying distances, making it a versatile choice for safeguarding premises. This mechanism differs from other options, such as sensing window breakage, which typically involves acoustic or vibration sensors rather than light interruption. Monitoring sound levels focuses on auditory detection and requires different technology. Sending alerts when doors open usually employs magnetic or contact sensors that detect the physical position of doors rather than relying on light interruption. Therefore, the correct function of photoelectric cells aligns specifically with detecting interruptions in light beams.