And, behold, the angel of the Lord came upon [him], and a light shined in the prison: and he smote Peter on the side, and raised him up, saying, Arise up quickly. And his chains fell off from [his] hands.
Note 3 at Ac 12:7: The light shining in the prison didn't wake Peter up; the angel had to hit him in the side. Peter must have been very sound asleep (see note 1 at Ac 12:6).
Note 4 at Ac 12:7: There is no mention here that the chains were unlocked. Apparently, Peter's arms were made to pass through the metal chains, much as Jesus walked into a room when the doors were shut (Joh 20:19).