I'm not planning to have one soon, but when I do.... can I use it to find out my friends secrets

Also, can just have a normal conversation with them in their non-lucid to:
a) tell them they are dreaming
b) secrets
c) other junk

But the thing is, they don't know that it is me ACTUALLY talking to them when they wake up. In other words, they have no idea they just spilt all their inner secrets to me and now I know..... don't tell them when it happens