Originally Posted by B747-437B

Not sure of the specific mechanism, aircraft types and pre-flight checklists you use, my airline has a specific preflight check item for BOTH cockpit crew and the purser to verify the flight deck door latching mechanism on ground, as well as to test the external override mechanism. If the door is not fully latched and latch engaged, there are two additional visual indicators that point this out to the crew (one each located inside and outside the cockpit) and verification of the external indicator is one of the pursers checks prior to notifying cabin secure.