On the inside of the room with the door closed the bolt is installed on the surface of the door next to the pocket. The strike is surface mounted on the jamb next to the pocket. It works like a rocker switch. When the button is pushed into the door, the bolt swivels and the other half pops out protruding from the door surface. This physically prevents the door from returning into its pocket because the protruding bolt will contact the strike. You will need to mortise into the door behind the bolt ⅝" deep to allow it to swivel. For emergency access a small hole can be drilled from the outside of the door. Then a slim object can be inserted through the hole to swivel the bolt back to it's flush position.