The important position and role of modern video alarm system in the definition of urban social security also largely defined between personal safety and national security, the public and public places, such as essential public infrastructure, transportation and daily social activities , should be incorporated into a range of urban security. In some special occasions with national security needs tools to burst fire, first aid, major criminal cases promptly sent police and armed police forces, rapid urban security to protect the normal order of life and property security and socio-economic and political life stable, for the masses to create a reassuring and comfortable urban environment. 1 The importance of urban security and background on the specific situation in China is concerned, the social demand for safe growing, mainly in the following two aspects: First, the international community in combating international terrorism, while important for the respective goal, an important unit and vital parts of general strengthening of security measures. China is now the police have decided to set up the air in order to enhance the safety of aircraft flight, which is to improve the intensity of anti-terrorist hijacking an important aspect. But the increase in the number of police in the preparation and not the only way to implement Kejichuangan, play a technical role of prevention is the fundamental way. Second is to increase residents generally increase and severe by the people's material and cultural living standards resulting from domestic public order situation of security requirements. 2 Urban alarm system applied leading-edge technology (1) The congestion level estimation system technology can be widely used in railway stations, airports, parks, Olympic venues and other large flow changes in place access control, can effectively avoid congestion and stampede; while the technology can also be linked with the air conditioning system, under different flow conditions control staff and air conditioning (air conditioning heat large materials research facility) of power, to avoid waste and save energy. This unique three-dimensional image analysis system, you can use two cameras, according to the mounting angle of the camera, the height estimates, subject distance and height of the object, further calculate the degree of congestion within shooting range. (1) moving object automatic tracking technology of the technology can be used over a wide area from the dome camera to automatically detect a moving person. In this case, the camera in the selected target can automatically track moving targets, and use large optical zoom 30 shooting to clear, enlarged picture. The technology can be widely used in streets, buildings, shopping malls, airports and other personnel action range big place, to avoid errors of manual tracking. (2) anti-shake image stabilization technology automatically through the entire screen of the motion vector is calculated because the shaking and deformation caused by electronic compensation of the image, you can get a clear image in the case of camera shake. This technology is particularly suitable for outdoor environments mounting the camera case at high levels, can effectively avoid the influence of strong winds or heavy rain caused by the occurrence of image blur blur. Avoid the plane, train, truck and other fast-moving objects, image blur by strong airflow caused by the impact, particularly suitable for installation in mobile command vehicles, tall outside the building, watchtower places. (3) The scene change detection This function is based on video motion detection basis, is a special kind of VMD (Video Motion Detection), its trigger depends on two conditions: most of the screen scene changes; changes after within a certain period of time does not detect moving objects. This technique is suitable for cameras malicious covered; the lens is sprayed; the camera is forced to change direction; with the lens is folded away or destroyed timely alarm signal promptly notify the duty to prevent the criminals take advantage of. (4) Super wide dynamic technology with a camera Super Dynamic features, with excellent double-speed CCD, can capture the video signal from the dark and bright parts and process them separately, so that the image regardless of the region (on a per-pixel) We can get the most appropriate clarity and brightness, extended dynamic range compensation range to 160 times. Particularly suitable for use in strong backlight situations, under the ever-changing high-contrast, weather, seasons and other natural environments.