With the distant keyless-entry systems that you find on cars today, security is a huge issue. If individuals could easily start other people’s cars in a crowded parking lot at the mall, it could be a real problem.
And with the proliferation of wireless scanners, you also ought to stop people from”capturing” the code that your transmitter sends. Once they have your code, then they can merely re-transmit it to start your car.
The recipient’s controller chip includes a memory location that holds the present 40-bit code. If not, it does nothing. After the transmitter sends a 40-bit code, then it uses the pseudo-random number generator to pick a brand new code, which it stores in memory.
On the other end, when the receiver receives a legal code, it employs the exact same pseudo-random number generator to select a new one. This way, the transmitter and the receiver are synchronized. The receiver only opens the door when it receives the code it anticipates.
It is not easy to hack this system. You can’t even open a key like this easily, unless you have Japanese scissors, but for any repair or upgrade you have to go to a special repairman.
If you are a mile away from the vehicle and inadvertently push the button on the transmitter, the transmitter and receiver are no longer synchronized.
The receiver solves this problem by accepting any of the subsequent 256 possible valid codes in the pseudo-random number order. However, if you accidentally push the button 257 times, the receiver will completely dismiss your transmitter. It won’t operate anymore.
But I really don’t know how you will menage to press a button so many times, the only time you can press one button so many times is when you play dragon dance slot.
So, what do you do if you desynchronize your transmitter by simply pushing the button on it 300 times, so the receiver no longer admits it? Most automobiles give you a way to resynchronize.
Here is a typical procedure:
Switch the ignition key on and off eight times in under 10 minutes. This informs the safety system in the automobile to switch over to programming manner.
Press a button on all of the transmitters that you want the car to recognize. Most cars let at least four transmitters.
Switch the ignition off.