The SD card size required for a security camera depends on the camera's video quality, frame rate, and recording duration. For example, a 150 GB SD card can store around 2-3 days of continuous video footage from a CCTV camera with a resolution of 1080p and a frame rate of 15fps. However, if you opt for lower video quality or shorter recording duration, the SD card size required would decrease accordingly. So, considering the other factors, you can choose an SD card within the range of 32 GB to 512 GB.