Half a croissant, on a plate, with a sign in front of it saying '50c'
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Random keypad

 for a safe or other code protected entrance
  (+17, -2)(+17, -2)
(+17, -2) 		  [vote for,
against]

Whenever you get these keypads to open a door with the numbers o to 9, the numbers of the actual combination get used and the others don't. So you see that the used keys are more well, used.

Either the numbers fade or the keys themselves show tell tale signs.

I propose random numbers on the pad.

So you have your basic calculator layout of 0 to 9. But all the numbers are leds that change p[osition every time you use them. The code stays the same but the numbers on the keys switch position randomly.

Each key now gets the same usage.

—zeno, Feb 27 2009

PIN Disguise PIN_20Disguise
[xaviergisz, Feb 27 2009]

sliding 15 puzzle http://en.wikipedia...wiki/Sliding_puzzle
you would have some dud extras to play with [wjt, Jun 02 2009]

[link]






       This sounds good, but the changing keys part might be a little expensive. Changing the code every now and then would be a better idea.   

       Or maybe you could have a code that uses one of each number. Of course, that limits the number of possible codes.
—Spacecoyote, Feb 27 2009
   

       Good idea for debit card PIN entry, this could prevent people in line behind you from being able to tell what you typed in by seeing where your finger went.   

       On the downside, you couldn't add Braille to the keys, but it would be good for home use.   

       I'll give it a +.
—paix120, Feb 27 2009
   

       Braille I/O devices exist, however, they're not cheap.
—Spacecoyote, Feb 27 2009
   

       //changing keys part might be a little expensive//   

       It wouldn't be expensive to have the keypad's numbers light up in different places. It's just some simple programming. He's not saying they move around mechanically.
—theleopard, Feb 27 2009
   

       I saw this baked about 10 years ago on the entry door of a facility I used to visit. The clear keys were also optically distorted so they were only readable in a very limited viewing angle. Laudably secure, yes; but really annoying to use. I'm not surprised that they didn't become popular. [+]
—batou, Feb 27 2009
   

       I love the link in the PIN_Disguise idea.
—theleopard, Feb 27 2009
   

       The burglar will hope for equal wear, remember: if they posit by the wear that you used a ten-digit code, that's only a keyspace of 10! (that's ten factorial, or 3,628,800) to search, instead of 10^10 (or ten billion.) Basically, using a ten-digit code with each digit once, on a ten-digit keypad, has the same security value of using a six- or seven-digit code.)   

       On the other hand, setting up a keypad to display digits isn't all that hard: you don't need little mini-LCDs on each key, merely one of the little figure-eight LED displays that 80% of us stare at in the middle of the night trying to figure out whether we've fallen asleep yet or not. If they *were* mechanical (which isn't that hard given that you already have wires running to them--probably quite a bit easier than driving a liquid crystal matrix, in terms of technology involved), you could read them by shape (not perfect for the blind, but not impossible either.)   

       On the other hand, you could just buy whatever technology an iPhone's display is composed of (or, if you're lazy, embed an iPod Touch into the wall, write a program that displays randomized digits, and have it send a signal on one of the charger/connector wires to the door lock motor if it's successful.) But if you're gonna do that, there are things with a much larger keyspace than digits to use-- why not draw a picture of something to get in?   

       Or, instead of looking up the technology ladder, we can look down: have one button. Make sure it's absolutely silent. Have people enter their passwords/PINs in morse code.
—derefr, Mar 01 2009
   

       Baked. I saw this at Oak Ridge National Labs back around 2001. Even better, the viewing angle on the keys was so small that anyone trying to spy on which numbers you used would pretty much have to be sharing your shirt at the time.
—PhaseShifter, Mar 01 2009
   

       I usually don't remember pins, but the shape they make on a keypad. [-]
—placid_turmoil, Mar 01 2009
   

       A binary version might do the trick.
—Spacecoyote, Mar 01 2009
   

       My financial institution has baked this at the log-in page to their online banking services. The PIN is entered by clicking on a randomly rearranged on-screen number pad. Being on screen means no keystrokes are recorded, and presumably the scrambling of the pad helps against other more sophisticated types of attack.
—BunsenHoneydew, May 31 2009
   

       This is one of those exceptions, that even if it's slightly baked - I like it [+]   

       I wonder if you could build an IR viewer that would see the residual heat from the previous ATM user's key presses.
—imho, May 31 2009
   

       Those sliding tile puzzles where you have to get the numbers in a pattern surfaced in my mind. Each button is a tile movable to the gap. You can switch the buttons to your heart's content.
—wjt, Jun 02 2009
   

       You could get around the key-wear issue by making the code always use all keys. In this case the number of combinations is n!, where n is the number of keys. So, for a 6-digit keypad, there are 120 posible codes - the downside is that you have to remember a 6-digit number, of course.
—hippo, Jun 02 2009
   
      
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