Quote:
Originally Posted by semtex
But why do you need to power the fob at all? You don't need to power it to start the car. It's passive RFID, and you can start your car -- fob in pocket -- even with the battery completely removed. The only thing the fob needs power for is for the lock/unlock/horn buttons to work, and to be able to lock/unlock the doors by just pressing the button on the outside of the door. Well, you're not going to be using the buttons on the fob while it's in the fobgina for obvious reasons. And there's no reason to get out of the car while the fob is in the fobgina to hit the external door lock button. I just don't see the functional value of the fobgina. It's not like it recharges a dead battery or something.
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That is not exactly true. You wouldn't want a passive RFID for your car, they are much easier to duplicate.
In this FOB, the car and the FOB exchange a sequence of encryption messages. Furthermore, the FOB never sends the car the same message twice. A microprocessor changes the sent message every time (based on an encryption key). This is the most secure method.