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Doors that shut on their own are designed that way for a reason: to prevent the spread of fire and smoke in a building. Sometimes you need to hold the door open temporarily, though, such as if you're moving furniture through the doorway. If you're in a pinch and you don't have a wedge on hand (the preferred method, see Warnings below) you can hold the door open with a coin.
Step 1Getting The Supplies
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Come on, if you don't have a quarter you are seriously poor (Euros work too.)
The point is if you carry furniture out through a door that closes back onto itself, such as a fire escape, the penny will serve to stop the door closing completely so that the lockin mechanism will not catch.
I can see this would be useful in situations where fire extinguishers, rocks and door stops cannot hold the dooropen maybe?
For instance, when carrying a sofa etc. from one building to another through a fire escape, and don't want to walk all the way through the building to unlock the door, or leave the door wide open for petty theives, the penny allows the illusion of being locked fora short amount of time until you need to reopen the door from the outside.
L
http://www.youtube.com/watch?v=1VrCzsx-OxA