Which device is not primarily a surveillance sensor?

The pressure pad is not primarily considered a surveillance sensor because its primary function is to detect physical pressure or weight applied to it, often used in security applications for triggering alarms or alerts. It serves more as a detection mechanism rather than providing the type of ongoing monitoring and observation typically associated with surveillance sensors.

In contrast, the devices listed as other choices are all designed with surveillance capabilities in mind. The Remote Video Surveillance System (RVSS) utilizes cameras to monitor areas and gather visual data. Magnetic Point Sensors (MPS) detect metallic objects or movements, which can provide information about activity in a region. Infra-Red Devices (IRD) detect heat signatures and can monitor for movement based on temperature changes. All these devices are integral to surveillance operations, making them distinctly different from a pressure pad’s primary function.