CompTIA: Advanced Security Practitioner (CASP) Exam Prep

Answer - A - Photoelectric intrusion detection systems can only be used in windowless rooms. This is due to this system detecting changes in a light beam. These system works like photoelectric smoke detectors, which emit a beam that hits the receiver. If the beam of light is interrupted, an alarm sounds. The beams emitted by the photoelectric cell can be cross-sectional and can be invisible or visible beam. Cross-sectional means that one area can have different light beams extending across it, which is usually carried out by using hidden mirrors to bounce the beam from one place to another until it hits the light receiver.