This little 'device' streamlines the process by pressing the right keys for you, and can be hidden in your palm so you simply mash your hand against the keypad and - apparently miraculously to anyone watching - unlock the door in one go.
Time to make: Less than 10 minutes
Time saved: About 30 seconds per day in my case; your mileage may vary.
Payback time: 20 days, in this case
Background: The research group I work in was moved to a new office. In the old place, I'd got used to an RFID card in my pocket allowing me to open the door just by leaning against the sensor, but the new office had a keypad on the door. It was going to use an extra 5-6 seconds every time I needed to get in the office!
There had to be a better way...
Step 1: Combinations Rather Than Permutations
First off, we realised that it was unnecessary to type the "C" (clear) at the start unless the previous person to try had entered the code wrongly. That cut maybe half a second off the time taken to enter the code.
But then we noticed something: the code had a sequence of digits ("132") that weren't in numerical order - yet when they were typed in numerical order ("123"), the door still opened. That is, this model of keypad is a combination lock rather than a permutation lock. It didn't matter what order you typed in the code, as long as you typed in all the digits that made it up. You could type "1-3-2-5-9" or "3-2-1-9-5" or "9-2-3-5-1" or any other arrangement.
The other crucial point was that these keys didn't have to be pressed separately - i.e. not only was there no requirement for the digits to be in the 'right' sequence, there was no requirement for there to be a sequence at all. Thinking about how a simple mechanical lock like this works, that ought to be obvious.
So, if we could press multiple keys at once, we could save a lot of time. If you angled your hand just right, it was just about possible to press all the keys required at once, but it was pretty awkward.
We really needed to make some kind of device which did that. But we couldn't just press all the keys, or press any wrong ones: whatever device we made needed to press only the right keys.
The simplest thing to do seemed to be to make something which, when held onto the keypad, pressed the right buttons.
Step 2: Working Out the Layout
Then, looking at how these were actually arranged, it seemed easiest to fill in gaps between adjacent keys that need to be pressed (second image).
And, to ensure that the device lined up correctly with the keypad, i.e. no incorrect keys were pressed, it seemed sensible to put a frame of sorts along two edges (third image).
Step 3: Making the 'keypad Masher'
I took a scrap piece of "Cay Foam", a plastic foam board which used to be available from C & A Building Plastics (though it doesn't seem to be any more) and cut it with a scalpel into a backing sheet, and individual strips and bits which could then be put together to make the right layout.
You could use thick cardboard, MDF, acrylic, anything - even a sheet of something with pins or nails stuck into it at the right points. If you have access to a bandsaw, router or milling machine you could produce something quite beautiful. The Cay Foam is ugly, but it was very quick to cut by hand, at my desk!
Mirroring the layout from the previous step, copy it onto the backing sheet, and then stick the strips/bits on in the right places. I used double-sided foam tape; you could use superglue or anything really; you may want the pieces to be repositionable at some point (e.g. if you make a mistake, or if the code is changed).
Step 4: Try It Out!
The first few times you might find it easiest to hold it between finger and thumb (first two images) to make sure you can line it up correctly, and to get a feel for how much force you need to use. But fairly soon you'll be able to palm the masher and hide it (third image). If you become skilled enough at doing it in a fluid motion, it really can look (to anyone else walking past) as if you're just slamming your palm against the keypad and somehow unlocking the door...
If you're so minded, it would be easy to improve the fit of the masher into your hand, giving it more comfortable edges or making it from something transparent or flesh-coloured so it's even easier to hide. Or make a set of keypad masher knuckledusters, where it looks like you're literally punching the keypad with your fist to get access. Or an elbow-pad!
Alternatively, you could stick the key-pressing bits on the back of a card which looks like some kind of official access card anyway, so that you appear to have a kind of contactless swipe card that simply needs to be pressed against the keypad.
Some risks: Don't label your masher with the code, or the room number. You're basically creating a device which changes the security of the keypad from a"what you know" method (a code) to a "what you have" method (a key). If you lose it, and it has the room number on it, then it's equivalent to losing a key with the room number written on it.
Be careful, but have fun!