Prayer Is Powerful Against High-Security Imprisonment

James and Peter were key leaders of the early church. During this time, King Herod arrested James and had him killed. When Herod realized that this act pleased the Jewish people, he sought to gain further favor by arresting Peter as well—likely intending to do the same to him. Peter was placed in prison under high security, guarded by 16 soldiers in four watches, with four soldiers each, while being chained.
King Herod held great power, and it seemed unlikely that anyone from the church could influence him to release Peter. The only option the church had was to pray—and that was powerful enough to break through even a high-security prison.

Our Duty Is to Pray with a Clear Conscience.

The church may have also prayed for James, and even Peter might have prayed for James rescue. Yet James became a martyr for Jesus Christ—this was within the sovereignty of God. Our duty is to pray earnestly and leave the outcome in God’s hands. Whether the answer is yes or no, we must trust God’s will, wisdom, and omniscience.
“Cast your burden on the LORD, and He shall sustain you.” (Psalm 55:22) “Pray without ceasing.” (1 Thessalonians 5:17)

Peter Thought It Was a Vision!

As recorded in Acts 12:9, when Peter was led out of the prison by an angel, he didn’t realise it was real. He thought he was seeing a vision.
when Herod was about to bring him out, that night Peter was sleeping, bound with two chains between two soldiers; and the guards before the door were [c]keeping the prison. 7 Now behold, an angel of the Lord stood by him, and a light shone in the prison; and he struck Peter on the side and raised him up, saying, “Arise quickly!” And his chains fell off his hands. 8 Then the angel said to him, “Gird yourself and tie on your sandals”; and so he did. And he said to him, “Put on your garment and follow me.” 9 So he went out and followed him, and did not know that what was done by the angel was real, but thought he was seeing a vision. 
Even the Church Was Astonished
After the angel left Peter, he went to the house of Mary, the mother of John Mark, where believers were gathered in prayer. He knocked, and Rhoda, a servant girl, recognized his voice but was so overjoyed that she ran to tell the others without opening the door.
They didn’t believe her. “You’re out of your mind,” they told her. But she insisted, and they said, “It must be his angel.” Only when they finally opened the door and saw Peter did they realize their prayers had been answered. They were astonished.
Perhaps they had expected God to answer in a different way—maybe through Herod changing his mind or some political shift. But God’s response went beyond their imagination.

God Overrides Human Expectations
“Now I know for certain that the Lord has sent His angel and has delivered me from the hand of Herod and from all the expectation of the Jewish people.” (Acts 12:11)
Herod and the Jewish leaders had hoped to harm Peter and suppress the church. But God delivered Peter and used him even more powerfully in ministry. Later in the chapter, we read that God struck Herod down, while the church continued to flourish under Peter’s leadership.

• Just an additional thought –
  Acts 12:10 – Now when they had passed the first and second guard, they came to the iron gate that leads into the city, which opened for them by itself;

An irondoor opened by itself (Automatically) may be the prototype of the automatic door which is common in the shops and mall.