Which of the following is a common type of sensor used in intrusion detection systems?

An infrared sensor is a common type of sensor used in intrusion detection systems due to its effectiveness in detecting motion and heat emissions from objects. These sensors are capable of identifying changes in infrared radiation within their environment, which often indicates the presence of a person or object that is not supposed to be there. This makes them particularly useful in security settings where the detection of unauthorized access is a priority.

Infrared sensors operate by monitoring temperature differences, making them sensitive to body heat. They can cover large areas and be configured to minimize false alarms from environmental factors. This characteristic positions them as a preferred choice in establishing security perimeters and monitoring restricted areas.

In contrast, other types of sensors listed, like humidity, pressure, and temperature sensors, serve different purposes. While they are valuable in various domains such as environmental monitoring or process control, they do not have the same immediate applicability in detecting security breaches as infrared sensors do.