Can Satan and the demons read our mind?
No, I don’t think they can but I don’t think they need to be able to.
What is in a person’s mind and heart comes out of their mouth and is demonstrated by their lifestyle and choices. It would not be difficult for a human to be able to discern the type and general topics of thoughts of another person if they were to spend any length of time observing them live.
Matthew 15:18 But those things which proceed out of the mouth come from the heart, and they defile a man. (NKJV)
Whatever is inside of our mind or heart will eventually be manifested externally and the dark forces of Satan will be there observing in order to accuse us before God and throw it back in our face.
Revelation 12:10 Then I heard a loud voice saying in heaven, “Now salvation, and strength, and the kingdom of our God, and the power of His Christ have come, for the accuser of our brethren, who accused them before our God day and night, has been cast down. (NKJV)
Now back to Satan and the demons… they are finite creatures. Yes they are powerful, even “fantastic” compared to humans, but they are still created just like us.
Satan is NOT God’s opposite. He was a “super angel” probably the greatest being God ever created. Rather than being satisfied with that, Lucifer ascended to heaven with the intent of raising himself to God’s level (Isa 14:3), a decision which caused him, and a third of the angels who followed him, to suffer the greatest fall from grace in the history of the universe (Eze 28:17).
Satan, nor the demons, can see into the heart and mind, nor are they ominiscient, omnipresent or omnipowerful. They are powerful, they are super intelligent, they are cunning and master manipulators. But they are finite, and they have limits.
Don’t worry about the demons reading your mind; worry about them using your sinful words and choices to manipulate you and put distance between you and God (with regards to intimate fellowship).