Satan cannot read minds. 1 Kings 8:39 indicates only God knows the heart of man.
1 Kings 8:39 Then hear thou in heaven thy dwelling place, and forgive, and do, and give to every man according to his ways, whose heart thou knowest; (for thou, even thou only, knowest the hearts of all the children of men;)
Scripture warns us to guard our hearts and to stay our minds on the Word of God. It is the Word of God which is able to quench all the fiery darts of the wicked one.
satan walks about as a roaring lion seeking those he may devour --- so he is on the lookout for those who are in a position to be pounced upon. We are warned many, many times throughout Scripture to be careful what we say. If the words that come out of our mouths are words from God, our adversary does not have a toehold in our lives.