Anyone worried about an unlocked door in a pressurised airframe,i suggest a try,to open it. Would need a long arm to twist it. We had many times,an Attendant telling about "howling doors". Press diff usually handles the problem at around fl150 or soon later,when climbing. Sometimes we used wet tissue,just to get rid of the whine. Old hands in the cabin,know the tricks. Saudia 1011 was a sad example of,how difficult it is to open the doors from inside.