Which pairing correctly matches motion detector types to movement orientation?

• A. Microwave detects toward, Infrared detects across
• B. Microwave detects across, Infrared detects toward
• C. Ultrasonic detects toward, Photoelectric detects across
• D. Photoelectric detects toward, Ultrasonic detects across

Answer: (A)

Movement orientation depends on how each detector’s energy is emitted and how movement changes that energy. A microwave detector sends a narrow microwave beam and detects changes when an object moves along the line of that beam toward or away from the detector. Infrared detectors (PIR) look at changes in infrared energy across their field of view, using a lens to create zones; movement across the field causes noticeable changes across those zones, making them most sensitive to sideways (across) movement rather than directly toward the device. Because of these distinct sensitivities, the pairing microwave detects toward and infrared detects across aligns with how these technologies behave in typical alarm setups. The other combinations mix up these directional tendencies in ways that don’t match how the sensors actually respond.