This paper addresses the problem of improving detection, assessment, and response capabilities of security systems. Our approach combines two state-of-the-art technologies: volumetric video motion detection (VVMD) and virtual reality (VR). This work capitalizes on the ability of VVMD technology to provide three-dimensional (3D) information about the position, shape, and size of intruders within a protected volume. The 3D information is obtained by fusing motion detection data from multiple video sensors. Other benefits include low nuisance alarm rates, increased resistance to tampering, low-bandwidth requirements for sending detection data to a remote monitoring site, and the ability to perform well in a dynamic environment where human activity and motion clutter are commonplace. The second component of this work involves the application of VR technology to display information relating to the sensors and the sensor environment. VR technology enables an operator, or security guard, to be immersed in a 3D graphical representation of the remote site containing the video sensors. VVMD data is transmitted from the remote site via ordinary telephone lines, and displayed in real-time within the virtual environment. There are several benefits to displaying VVMD information in this way. Often, raw sensor information is not ina form that can be easily interpreted and understood-especially when taken out of the context of the sensor environment. Because the VVMD system provides 3D information and because the sensor environment is a physical 3D space, it seems natural to display this information in 3D. Also, the 3D graphical representation depicts essential details within and around the protected volume in a natural way for human perception. Sensor information can also be more easily interpreted when the operator can ''move'' through the virtual environment and explore the relationships between the sensor data, objects and other visual cues present in the virtual environment. By exploiting the powerful ability of humans to understand and interpret 3D information, we expect to 1) improve the means for visualizing and interpreting sensor information, 2) allow a human operator to assess a potential threat more quickly and accurately, and 3) enable a more effective response. This paper will detail both the VVMD and VR technologies and will discuss a prototype system based upon their integration.