A volumetric motion sensor is designed to:

• A. Detect intruder motion within the interior of a protected space; may be active or passive.
• B. Detect exterior perimeter movement only.
• C. Detect temperature changes.
• D. Detect sound.

Answer: (A)

Volumetric motion sensors monitor a three-dimensional space inside the protected area, looking for movement as a person or object passes through the defined detection volume. They can operate in different ways: a passive option detects changes in infrared energy from warm bodies moving within the area, while an active option emits energy (like microwave or ultrasound) and senses reflections or Doppler shifts caused by movement. Because of this, they’re designed to detect intruder motion inside the interior, not just along the exterior perimeter. They aren’t intended to detect temperature changes or sounds, which are the domain of heat detectors or sound detectors, respectively. This combination of interior motion detection and the ability to be either active or passive is what makes a volumetric motion sensor the right choice.