How Does The Remote Locking Protect Itself

[hertsnminds]

Following on from a comment about the alarm going off if you lock the car too soon after closing the doors I was wondering just how the remote locking protects itself.

In some systems a rolling code is used, where the car or key generate a new code every time the car is locked and this will be used to unlock the car. However, if this is how the C3 works then how does the spare key know what the new code is? I have tried locking with 1 key and opening with the other and this works so clearly no unique code has been sent to the key or if it has just sending a barrage of codes (or an override code) to the car can unlock it.

In other systems the code is hidden in a wide bandwidth signal so it is not easy to tune in and steal the code. In these systems the same code is sent every time just in a different part of the frequency band.

We also know that if you park a couple of Pluriel close to each other and unlock 1 of them the alarm of another will be set off.

So the question is does anyone know what trick the Citroen system uses?

Ian
Orange 03 Senso