Yes, cats can develop a 'resistance to the CatScram cat repellent. This type of response to the CatScram is not common, but does happen occasionally. Perhaps an explanation of how the CatScram repellent works will be helpful.
The CatScram cat repellent works primarily on fear. Cats are easily startled animals and a sudden loud and offensive noise like that produced by the CatScram is very frightening to them. Their self preservation instincts kick in an tell them to avoid the area protected by the CatScram.
Because some cats are more fearless than others, they are willing to brave 'danger' posted by the CatScram cat repellent. Once they do this a few times and discover that they will not be harmed by the CatScram, they just begin to ignore the CatScram altogether.
If a cat loses it's fear of the CatScram cat repellent, it can be difficult to regain. However, many customers find success by relocating the CatScram, taking it away for awhile, and trying other methods of changing the environment around.