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The efficient transmission of video rate data is a demanding need in camera surveillance systems. This paper presents a low power smart CMOS image sensor which is suitable for surveillance applications. The sensor captures the image scene and using in-pixel difference detectors, it detects the temporal change events in the image. To reduce the power consumption, only the portions of the image scene with intensity change are transferred to the output. For this purpose, the performance of two different event driven data transfer methods, pixel based and window based, are investigated and it is shown that each method is appropriate under different surveillance conditions. The performance of the technique is shown using a 64×64 pixel sensor designed in a 0.18μm standard CMOS technology. The sensor chip consumes 0.5mW of power while operating at 30fps.