Electric bolts are an efficient method of adding secure access control to a door.

An electric bolt will protrude out as long as there is power being supplied and then detector plate is present.

For a "Fail Safe" setup, when the button is activated, power supply then releases power from the lock, and if power is lost then the lock also releases.

You would connect the control device and power to the bolt via an access control panel, relay or exit button so that the power can be cut when triggered. When powered up again the bolt protrude again locking the door in place.