Instructables

Car fob for house doors?

I've seen a couple different examples of re-purposing things like wireless doorbell ringers or other devices to activate a door look solenoid but i don't want to carry any more stuff in my pockets.Ii was wondering if it's possible to use a car fob to do the same thing?


i would love to map the door lock button on my car fob to unlock my front door and vice versa for the lock button.  I know for garage door openers in your car you can hold down the OEM remote and it syncs the signal not sure if there is a way to do this with my car fob.


Sadly, I don't think that the carcodes are compatible with other receivers. There is a system called "Keeloq" which you CAN buy which uses a similar protocol to cars, but I suspect the actual car system is different.

It MIGHT be worth taking a chance, and buying a Keeloq compatible receiver and trying it.
To my superlative suprise THIS MIGHT ACTUALLY WORK
http://en.wikipedia.org/wiki/KeeLoq
SpinningCone (author)  steveastrouk2 years ago
hmm looking at that Keeloq is used a receiving cypher for some cars but unless my car was also Keeloq probably wouldn't work. guess i need to snoop around for some documentation on what my car fob sends or find a cheap way to sniff it .

Yes, there are probably other rolling codes available, but the protocol itself might be secret.

Steve
SpinningCone (author)  steveastrouk2 years ago
protocol should be Irrelevant for my application no? i just need to be able to differentiate one signal from the other and perform one action or another. any actual data within the signal i shouldn't need, just that i can recognize the signal as unique and use that as a trigger.
Sadly, not no ;-)

The code transmitted changes EVERY time you press the button, in a way the receivers understand, but is not public knowledge. So you can't tell its "yours", unless you know what yours is sending.

Catch 22.

Steve
i dont think that is completely true...if it was, then theoretically if you have 1,000 cars in a walmart parking lot and you press the button on the fob 1,000 times, you would in eventual time be able to unlock every car in the parking lot every time.

The reason i bring this up is because this reminded me of something i read in my Ford Focus owner's manual. I ran by something in the manual that talked about the locking mechanism, and it stated something along the lines that if you buy an extra fob AND key from Ford, they have to program the fob to the vehical's "signature" (for lack of a better term). its a pre-set security code, or something of the like that is programed into the vehical's computer that it recognizes. i am pretty sure that this transmitted code you speak of doesnt exist cause refering back up to my hypothetical scenario, you could unlock every car in a parking lot...but who in the hell would wanna waste their time like that?...lol
Not true at all. The keyspace permitted is huge - 2^64 possibilities at least, thats 1.8 and 19 zeros of possible codes. Not even Walmart car parks are 10^12 times bigger than your postulated car park, and neither can the keyfob radiate several megawatts to catch every car in the park..

The dealership programming is effectively the resyncing of the keys and the code, which is locked from mortal access.

Steve
I understand that the fob only has a small radius...thus the reason why i can unlock my car only from 20' away in a clear, unobstructed area...and only 5-10' with an object obstructing the way. Remember that i used a hypothetical conclusion. i did NOT in any way hint at the method of unlocking any of the vehicals in said parking lot, but keeping out the severe complicated factors you are throwing in and simplifying it, thats how i made my hypothetical situation.

I read up a little on the key fob to edumacate myself, and found out that we are both right. so heres to agree to dis-agree.

IT IS POSSIBLE to unlock another person's car with YOUR key fob, however it is unlikely. The key fobs of today use 40 bit x-mission codes with 256 levels. this means that there are trillions of possibilities. It is possible to de-syncronize the fob from the car thats what the 256 levels come in. if you press your button 256 times and your not near your vehical, you will still be able to request a fuction from it, but if you press it 257 times your car will ignore the fob untill you re-sync it. of course you know this already steve, so i dont have to tell you, however some other person might find the info useful.

Now as far as re-programing the fob or the key for that matter, you CAN go to a dealership, HOWEVER it would be a waste of time and money to do so as you can simply do this at home. i found out i can re-program my fob and key by using the steps stated in my owner's manual. pretty much all vehical manufacturers provide this convenience.

But either way, i vote to agree to disagree, for some points on both sides are true
What stops you unlocking your car at the same time ?
SpinningCone (author)  steveastrouk2 years ago
reversed buttons. the car *lock* is door *unlock* and vice versa. so when i get out of my car at home and lock the car the front door is ready to open. when i leave the house and unlock my car the house locks.


potentially i could use the trunk button as a back forth (lock unlock) function which would also work great since you have to hold the trunk button for a couple seconds so short pulses wouldn't affect the car
(I have this mental image of him pressing the button on his fob, and all the house lights blinking as the doorbell rings.)
Fortunately, it won't work like the "invention" featured on an old show: All in the Family, years ago, that rang all the doorbells on a city block (was supposed to only ring the one nearest you, if raining, so you didh't have to get wet before finding out that no one was home). Tis what I thought of first though :-)