Answer:
D. They are foolproof
Step-by-step explanation:
The intrusion detection systems can tell you if there is an intruder but the action after the detection to stop the intruder is made by humans. Depending on the technology used in the system, the false alarm can be created by different situations. For example, an infrared detector can be affected by the weather and send a false alarm. The detectors need to be plugged into a constant power supply to work. But the systems of intrusion detection aren't foolproof.