Nuclear technology is being promoted and applied worldwide but poses a certain threat to public safety, thus necessitating nuclear radiation detection. In addition to the use of dedicated instruments, the use of surveillance cameras with complementary metal oxide semiconductor (CMOS) sensors is a promising direction for nuclear radiation detection. Currently, such use requires masking the camera lens or working under a static environment, conditions under which a camera cannot perform surveillance monitoring. In this article, we propose a method for detecting nuclear radiation based on an uncovered CMOS camera that enables nuclear radiation detection while the camera is in surveillance monitoring mode. First, we captured videos without covering the camera lens of irradiation from a 99mTc radioactive source. Then, an inter-frame difference algorithm and Gaussian smoothing method were used to reduce the interference of moving objects and visible light on the images. Finally, a series of thresholds were selected to test the validity of our detection method on a validation set. The experimental results indicate that the proposed method can effectively detect nuclear radiation. It is further verified that the surveillance camera can perform surveillance monitoring and radiation detection simultaneously.