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This prank door latch can be opened by turning the knob
clockwise, or by turning the knob counterclockwise,
*almost* like a regular mechanism.
However, at any given time, *one* of those two operations
(clockwise or counterclockwise) will be useless: the knob
will spin freely instead of opening
the door, and the other
operation will work properly.
Every time the door is closed, which operation properly
opens the door, and which operation freewheels, will
So if walk up to the door, and open it by turning the knob
clockwise, then close the door, and attempt to turn it
clockwise again, the knob will spin uselessly. If I then turn
the knob counterclockwise, I can open the door.
Three way door knobs.
[2 fries shy of a happy meal, Jun 16 2017]
Two door knobs
[pocmloc, Jun 16 2017]
||[+] Bonus feature: keeps Alzheimer's patients occupied for hours...either inside, trying to get out; or outside, on the lam from Nurse Ratched.
||Improvement. Wrong way locks door for 5 minutes.
||Noice. You should be able to cannibalize one of these, [link], to get some frustrating combinations.
||Fit the door with ten identical knobs. Only one opens the door. The other 9 spin freely. The reset mechanism randomly changes the active knob each time.
||Probably not going to sell many of these in high-rises at the moment.