Final answer:
Magnetic contact sensors and infrared motion sensors are commonly used to protect a perimeter door. Infrared motion sensors use beams of infrared light to detect movement near the door.
Step-by-step explanation:
The two sensors commonly used to protect a perimeter door are magnetic contact sensors and infrared motion sensors.
Magnetic contact sensors consist of a magnet and a sensor that detect when the door is opened or closed.
Infrared motion sensors use beams of infrared light to detect movement near the door.