Volume monitoring
In alarm systems, volume monitoring is the name for a monitoring principle in which the entire interior of the space to be protected (volume) is monitored for moving people (or animals and objects) by sensors .
In contrast to this, there is the monitoring of the outer skin , in which only the edge area of the room, mostly its entrances (doors, windows), is monitored, but you can move inside without being disturbed.
Typical sensors for monitoring volume are passive infrared - motion detector and active ultrasonic sensors , for a perimeter protection switching contacts and glass breakage detector .
Depending on the design, light barriers can be used for both purposes.