Does Satan know what is in people's hearts? And how do we know that Satan is far from us? And what is the evidence for that?

Allah alone knows the secret and what is even more hidden. As for Satan, he does not know the thoughts of people's hearts unless they utter them or act upon them. He is only capable of whispering and plotting. Satan is driven away from a servant by their uprightness, frequent remembrance of Allah, the tranquility of their heart, and the recitation of the Qur'an, especially Surat Al-Baqarah. Whenever a servant remembers their Lord, seeks refuge in Him, or recites the Qur'an, Satan retreats and distances himself.