Which device is commonly used for recording video footage in surveillance systems?

The correct answer is DVR, which stands for Digital Video Recorder. This device is specifically designed to capture, store, and manage video footage from surveillance cameras. It digitally records the video data, allowing users to easily access, review, and store video recordings over time. A DVR is essential for any surveillance system as it enables the effective monitoring and reviewing of footage for security purposes.

While other devices play important roles in surveillance systems, they do not specifically serve the primary function of recording video. For instance, a multiplexer can facilitate the simultaneous viewing of multiple camera feeds, but it does not store the footage itself. A computer can be utilized to process and view video footage, but typically, it requires the integration of a separate DVR system to function effectively as a surveillance solution. A monitor displays the video feeds or recorded footage but does not record video on its own. Thus, the DVR is specifically tailored for the role of recording, making it the most accurate choice in this context.