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Why would our front door have opened by itself? It was locked. It has an entrance set - a latched, not deadbolt, knob handled, keyed on the outside and turnsnib on the inside style lock. We have had a 40 degree Celsius day and the aircon had been on all evening and there is a bit of wind outside. The door opens inwards.

Donna
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    Is it possible the latch was not fully engaged? – The Evil Greebo Jan 04 '13 at 15:26
  • Possibly, at least I hope so, being after midnight that it happened. I remember going out the front door a few hours earlier to check the mail box so maybe that could be why. – Donna Jan 04 '13 at 15:39
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    Ghosts? No, the answer is clear: the door wasn't latched. The pressure imbalance between the inside and outside prevented a full latch and it eventually blew/sucked open. – Matthew Jan 04 '13 at 19:40
  • I think it was ghosts, or dead pirates, maybe a zombie??? – shirlock homes Jan 04 '13 at 21:22
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    Thanks everyone for your answers. I was thinking it was the not fully latched and pressure imbalance reason. I survived the night without a zombie eating my brains, thanks shirlock homes. – Donna Jan 04 '13 at 23:48

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Because although it was locked, the latch was not fully engaged. If it was very cool inside and very hot outside, especially if there was any humidity, I'm not surprised to hear that the latch didn't click into place the last time it was closed.

Amanda
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  • This is why most modern entries have both a deadbolt and a latch. The deadbolt is positive locking, not dependent on a spring latch to drop into the strike plate pocket, leaving your door unlocked if you fail to pull the door to the jamb properly. – Fiasco Labs Oct 24 '15 at 17:41