And suddenly there was a great earthquake, so that the foundations of the prison were shaken: and immediately all the doors were opened, and every one's bands were loosed.
Note 5 at Ac 16:26: This earthquake didn't just happen naturally. This was a mighty demonstration of God's power, and it was released because of the apostles' prayer and praise. Praise is a powerful force that can cause earthquakes or whatever miracle we need.
Note 6 at Ac 16:26: All these prisoners were set free, yet they didn't leave. They had already been freed spiritually by the faith they heard in Paul and Silas. When people truly experience the freedom inside that only God can produce, things that they previously would have given anything for suddenly become unimportant.