CompTIA Security+ Exam Prep

Answer: C - Photoelectric devices are smoke-activated detectors and are good at early warnings. These devices can be used to sound a warning alarm before the suppression system activates. These devices are also known as an optical detector, detecting the variation in light intensity. The detector produces a beam of light across a protected area and if the beam is obstructed, the alarm sounds. Another type of photoelectric device samples the surroundings by drawing air into a pipe.