Praying Aloud or Silent

Genesis 24:45
"And before I had done speaking in mine heart...."

Jesus prayed out loud in Matthew 26:39,42, 44; Mark 14:35, 39; Luke 22:41-42; John 17:1-26

Luke 18:10-14
"Two men went up into the temple to pray; the one a Pharisee, and the other a publican.
The Pharisee stood and prayed thus with himself, God, I thank thee, that I am not as other men are, extortioners, unjust, adulterers, or even as this publican.  I fast twice in the week, I give tithes of all that I possess.
And the publican, standing afar off, would not lift up so much as his eyes unto heaven, but smote upon his breast, saying, God be merciful to me a sinner.
I tell you, this man went down to his house justified rather than the other: for every one that exalteth himself shall be abased; and he that humbleth himself shall be exalted."
(they both prayed out loud.  Should Jesus have commented on staying quiet if that was important?)

I've heard people say that they don't pray out loud because they don't want satan to hear them.  Yet, those same people probably believe that satan can put thoughts inside their heads.

The scriptures don't specifically say satan (and angels) can or cannot hear our thoughts.  Yet, in Daniel 10:7 Daniel heard and saw things  and a spiritual being that others did not.  So, that seems to indicate that it all was done by thought processes.

Joseph heard from an angel in his dreams in Matthew 1:20.  In Acts 10:3 Cornelius saw and heard an angel in a vision.

If satan and his demons cannot read our thoughts then we can probably assume they also cannot transmit thoughts into our heads.  That means that whenever we hear a "still, small voice" then we will always think it is God's voice.  I know I cannot believe all communication I receive is only from God.

What did Paul infer in 2Corinthians 11:3 "But I fear, lest by any means, as the serpent beguiled Eve through his subtilty, so your minds should be corrupted from the simplicity that is in Christ"?

I firmly believe that some fortune tellers, witches, psychics, and the like get at least some of their information from the demonic realm.  Ask one of them how it is communicated.  What does it mean "familiar spirits" in Isaiah 19:3?  Take a look at 1Samuel 28:7-20.

I wouldn't be so sure that the demonic realm cannot hear our thoughts if I were you.