Acts 12:4

‘And when he had taken him, he put him in prison, and delivered him to four quaternions of soldiers to guard him, intending after the Passover to bring him forth to the people.

So Peter was taken and imprisoned, probably in the Castle Antonia, and he was placed under a secure guard of four squads of four soldiers each, rotating in three-hour shifts day and night, with two of them chained to Peter at any one time. Escape or rescue was therefore an impossibility - to man. His intention was to bring him out once the seven days were over.

The excessive precautions taken indicate Agrippa's determination to destroy Peter, and reveal his view of how dangerous the Jerusalem church was. He had no doubt been warned how Peter, together with his companions, had previously managed to escape and he wanted to ensure that it did not happen this time. (Incidentally this strict treatment helps to confirm that there must have been a previous escape, otherwise why the precautions?) He wanted to ensure that he kept the people of the Messiah in chains.