# car combo door locks... what's with the buttons?

I frequently see newer cars and trucks, which, instead of having a keyhole to gain entry, have an electronic combo pad instead (or in addition to the keyhole). Each button has two numbers on it, instead of one, like this:

[0-1] [2-3] [4-5] [6-7] [8-9]

My question is why do the buttons have 2 numbers each - i.e. the first button represents the numbers 1 and 2. It seems like one button covering two numbers is just not necessary. If I were to sit in front of the car, it is simply a matter of pushing the buttons in the correct order to unlock the car. The labeling of the buttons could be in a foreign language for all I care.

My guess is that the auto makers do this to say their locks are ultra safe because they have x number of (mathematical) combinations since each button has two values, while they are really limited to their number of physical combinations, which would be a lesser number.

My WAG has always been that it’s done so that owners can use any combination they want and aren’t limited to 1-5. (More than half the time, people choose birthdays as numeric passwords.)

I have no firsthand knowlege, but each button may be a rocker switch that can go towards either number…

Yes, if it’s what I’m thinking of, it basically is like a rocker. And it’s nothing new, either. I’ve seen these sorts of numeric keypads since at least the early-90s on Lincoln Town Cars.

I have an old lincoln and it’s not a rocker switch. One button represents two different numbers. I think the reason was as the OP guessed.

The keyless entry systems do not replace mechanical keyways-they are a supplement. Some touchpad keys are able to submit a dual input value, other don’t.

The difference in mathematical permutations is no different than the number of key wafer or pin positions, modified by the number of lift variants for the system extant.

The only blessing is if you’ve been a meathead and locked your keys in a car with touchpad entry, you can save a service call charge.

I like having them for that reason, and so when I go anywhere that I would be screwed if I lost my keys ( beach, etc ), I can put them under them in the trunk and ge them when I come back.

I think Ford (and Lincoln and Mercury) are the only cars that don’t have them. My car does.

They’re NOT rockers. Ten buttons would be too many. But you need 0 through 9. It’s actually all good user interface (too bad Ford interiors aren’t so well designed – I hope we learn something from Volvo, which are really nice).

Aside from your keyfob, you can (1) unlock the driver door, (2) unlock all doors, (3) open the trunk. If you car remembers driver profiles like mine, then (4) you can program two sets of codes, so that the seats, mirrors, presets, temperature, measurement system, suspension control, steering effort, and current display adjust to where they were last left by the then-current driver.

What’s really, really super is when camping/canoeing/whatever, I can toss the keys in the glove box, lock the car, and not have to worry about paying exhorbinant sums of money to OnStar just to open my locks.

For what it’s worth, my 2000 Ford Explorer has a keypad. Otherwise, what Balthisar said.

I would like to point out that the keypads are really not secure. 2600: The Hacker Quarterly magazine did an article about 10 years ago wherein they listed the total number of combinations possible for similar door keypads. A determined thief could run through all of them in less than half an hour. Also, it seems that when a car begins to develop electrical problems, the keypad is one of the first things to go.

But does a car lock allow you to try so many combinations? Most electronic devices are programmed to lock up or slow down after several incorrect entries.

Getting back to the OP, I’d like to point out that telephone keypads have 4 characters per button (one number and 3 letters) for the same reason: so you can use any easily remembered sequence.

Ford has had them for a while. My 1989 Supercoupe has keyless entry. My 1994 Thunderbird doesn’t. I don’t think the majority of Fords have them, even though it’s an option.

I doubt that. I was running through the possible numbers on mine and gave up at 13999 after about 15 minutes. That’s basically just getting started. (I later found out the code by looking on the computer in the trunk.) There are 5 digits and 5 possible values for each digit, leaving 3,125 possible combinations. I think the fastest you could do it would be roughly a combination every 3 seconds, which would take around 2 1/2 hours. Of course since the door will still unlock if the password is the last few digits you type of one guess and the first few of the next guess, it shortens the time a little, but I think the quickest thieves will still take over an hour with the average code. My keyless entry allows you to set a personal code in addition to the default code, and a lot of people pick a code that isn’t very hard to guess, but that’s a flaw with that person’s password picking skills, not the device itself.

While I haven’t put it to the test on a large number of vehicles, I’ve not found any that cared about the number of times you tried punching in numbers. Certainly, the ones on my Lincoln didn’t care.

Yes, but if you think about it, there’s only 5 pads to press. 0/1 is one button, so if the combination is 1110, you’re just hitting the same button over and over again. Instead of looking at as 10 digits, look at it as only 5. I don’t have the article any more, but the possible combinations filled two digest size pages.

Well I’ve had two new Lincolns since 1995 and never had a problem with the key pad. (or any other problem)
I like the key pad and one thing for sure… I will never be locked out of my car with the keys inside it.

Also must not be a problem with security or Ford would not continue to use them.

I did assume 5 possible digit values. And you only put 4 digits in your code, but my SC code is 5 digits. 5 ^ 5 = 3125.

Well, it’s doubtful that a thief would have much opportunity to run through the possible combinations undetected. Also, I’d imagine that it’s not something which would occur to most people. After all, the article appeared over 10 years ago in an obscure publication and the companies which market the locks have aggressive advertising campaigns. Nor do I think that it’s going to occur to the average person that if they just start punching numbers on the keypad that they’ll get lucky.

snailboy, the code on my Lincoln was only 4 digits, IIRC, and odds are, that a person isn’t going to have to run through all the possible combinations before they find the right one.

Given a truely random code, on average one will have to guess half the possible codes before getting the correct one. That’s why I said on average it would probably take about an hour to figure it out, when it would be 2 1/2 hours to go through all codes. (I earlier explained something else that makes it shorter too.)

I’m surprised yours only has 4 digits. That drastically changes things, with only 625 possibilities. You probably could guess them in less than 30 minutes that way even if it takes 5 seconds per guess (which is more realistic than 3 seconds). That’s a lot less secure than mine. It also allows people to put in their birth years and it won’t take long to go through all the possibilities. What year is your Lincoln out of curiosity?

Well, it’s gone to that great scrap yard in the sky, but it was a 1988 Lincoln Continental. I strongly suspect, however, that it was just a rebadged Edsel.

Just to demonstrate my earlier point too, suppose your code was 99971. This would be one of the last codes you guessed. However…

19997 19999

You see the code within the above two guesses?

1(9997 1)9999

The last one would be your 625th guess if going in order. That’s a lot different than it being your 3105th guess. I’ve figured that it would only take 625 guesses to guess any code with a digit 1 in it whatsoever, except 99991. Fairly interesting, eh? I think I may want to do some soldering and change my default code to something without 1 or 9 (in case someone went backwards).