How can I alert myself if my business bathroom toilet is overflowing?

My business bathroom toilet unexpectedly overflows, there is a problem with the main line in the plaza. The flush does seem weaker, but it will flush leading us to believe it is not clogged. I have a camera facing the bathroom door, but it is black/white when the lights are off making it impossible to see remotely if water is overflowing. Anyone have any suggestions on how to be able to monitor the issue through my camera?

Example ideas/solutions:

1. Turn off the water valve manually every night. *Tedious and employees likely to forget
2. Stand a small piece of paper/tissue, in view of the camera, vertically on the floor so that if it does overflow the paper will lay flat in my camera view. *Honestly my best idea but could also trigger false flags.

Any devices or solutions?