Hidden camera data storage required is different for each product. There are different resolutions and video compression formats which can significantly impact the duration of footage you can record. Furthermore you should take camera battery life into the equation as well. On a portable hidden camera with less than 2 hour battery life, it may not always make sense to have an SD card that stores more than 2 hours of video footage.
Check your camera specifications to learn which compression method it uses, then use our Video storage calculator tool to estimate how much disk space you require for your particular needs.