What do you mean, CoM, when you say "private conversation with the Lord"? Prayers unspoken? Or prayers spoken? If the latter, you're expecting God to prevent any demons from hearing? Even though everyone else on this thread believes demons do hear?
We've failed to find Bible guidance on the OP.
idea
Satan is a liar. When he lies he speaks his native language, and there is no truth in him.
You belong to your father, the devil, and you want to carry out your father's desire. He was a murderer from the beginning, not holding to the truth, for there is
no truth in him. When
he lies, he speaks his native language, for he is a liar and the father of lies.
John 8:44
As true worshipers we will worship in spirit and truth.
Yet a time is coming and has now come when the
true worshipers will worship the Father
in spirit and truth, for they are the kind of worshipers the Father seeks.
John 4:23
It is possible that when we pray to our Father (even out loud). Satan can not understand the language for it is spirit and truth, which Satan might not be able to understand (to him a foreign language).
Now if this is true with Satan how much more so with his demons since they are under him.
A student is not above his teacher, nor a servant above his master. It is enough for the student to be like his teacher, and the servant like his master. If the head of the house has been called Beelzebub, how much more the members of his household!
Matthew 10:24-25