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keyless ignition ? Answered

My car already has keyless door locks. I am just looking for a keyless ignition. Doesn't have to be the same system or fob as the windows and door lock. I can install a push-button ignition switch, but I want a security circuit like the newer cars that requires the presence of a fob (in your pocket) for the car to be able to start.  The instant on-off button isn't a problem, but you need everything that goes off when you would turn the key off to go off when you leave the car, not when you push the (on)-off button. It's going in a pristine old "93 Town Car that still has all it's bells and whistles working. I think working this into the existing door/window system would be a nightmare, so I'll keep it separate and be satisfied with a second fob. So, I need some help. Should this be a passive system sitting looking for an RFID or active with something like a bluetooth transmitter in my pocket? I know I can buy a kit, but there's no satisfaction in that. I'm not really constrained by a budget, but obviously I don't want to go over the market value of the car (tho it's worth a lot to me).


Besides the very valid points from @canucksgirl there is a very real security issue with simply using RFID or bluetooth. Unless you spend the time and/or money to secure the connection those types of connections are inherently insecure. I believe that basic RFID systems actually broadcast the code they are looking for. Don't quote me on that but I believe its the basis of the Universal RFID Keypad instructable.

The only 'hard' part would be if the original car was computerized enough to require an 'active' or programmed key -- if they key is chipped it will be a PAIN to bypass, because the car will constantly think its being hotwired.

Starting a car without the key is as simple as connecting the lugs in the order the key switch would, normally

Off - everything off
Accessory - power only accessories
Run - accessory + ignition run
Start - momentary contact that disconnects accessory but connects run and starter.

each would be a separate relay - accessory could run through the 'nc' of the starter relay so when you start (and it goes to the 'no' contact) it kills the accessories.

As for the logic - any of a thousand methods - passive rfid, active rfid, a bajillion radio protocols, a keypad password, a thumbprint scan, a secret knock, a hidden magnetic sensor...etc.
All the solutions would want a low power uC to do the thinking.

I'm not sure what the best way to go is, but make sure you consult with someone regarding insurance etc. Any modifications have to meet with some standards, otherwise, if your DIY method doesn't work properly and someone is able to steal your car, you might find your insurance is null and void. So its worth looking into.