Dear Marcus Dalley
Sometimes when people have something that doesn't quite work properly in their brains they get funny ideas, especially ideas we call paranoid ideas.
These ideas might be about people spying on them or listening-in to them. They become afraid that other people can hear their thoughts. Perhaps (they think) people are following them and trying to get their money. Or they can see them when they're in bed.
When this happens usually it's a sign that the person needs some medical help.
It's difficult for families when this happens, particularly if it's a new problem and it's never happened before.
When it does happen the first thing that most families do is to think that they need to demonstrate that there's nobody watching or whatever. They try so hard at this that often they finish up seeming to actually believe that those things are happening.
When you come to realise that maybe it's part of an illness someone might have (like schizophrenia, for instance) then you realise that there's no point in putting a lot of energy in dealing with those ideas themselves--because they're not based on reality anyway. You have to find other ways of dealing with the person. Sometimes this is tricky and often you need help from a professional person.
The sort of problem your uncle has is usually caused by something not working properly in the brain. There are some very good medicines that can help that.
In the meantime, if you are worried about his behaviour, talk about it with your parents. They will probably already know something is going on.