Which device is designed to open or close a circuit in response to a disturbance?

The device that is designed to open or close a circuit in response to a disturbance is the sensor. Sensors are crucial in alarm systems as they can detect changes in their environment, such as motion, heat, sound, or specific energy signatures. When a sensor detects an event—like motion in a secured area or a door being opened—it triggers a response, which typically involves closing or opening an electrical circuit. This action is essential for activating an alarm or notifying the control panel of an intruder, thus helping to maintain the security of a premises.

Other devices like control panels, keypads, and monitoring stations serve different roles within an alarm system. Control panels manage the overall system, receiving signals from sensors and determining subsequent actions. Keypads are primarily used for user interaction, allowing individuals to input codes to arm or disarm the system. Monitoring stations receive signals from the alarm system for continuous oversight but do not engage directly with environmental stimuli in the way that sensors do.