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I am just wondering why other keyfobs do not open my car door and thought every signal would have to be unique.

So I did some research and they use a rolling code so in fact the code changes with each use Why would this be anymore secure than having a unique transmitter and receiver for each car since with a rolling code change the keyfob needs to do it every time?

If I loose my fob and get my spare how does my spare then know what the code was?

I did my research on "How Stuff Works" but it raised more questions to me than it answered.

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With a rolling code system, both the transmitter and receiver calculate a code based on stored information that is not transmitted. Once the transmitter and receiver are "synchronized," a new code can be calculated in a sequence such that both calculate the same code as the next valid code in the sequence. In order for more than one transmitter to work, there is a system to allow the receiver to deal with more than one valid sequence. There is also a system to account for a transmitter skipping codes due to transmitting codes when out of range.

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So I did some research and they use a rolling code so in fact the code changes with each use Why would this be anymore secure than having a unique transmitter and receiver for each car since with a rolling code change the keyfob needs to do it every time?

The trouble with transmitting the same code every time is replay attacks. The thief can stand near you as you lock your car and record the code. Then after you walk off they can replay the code and unlock your car.

If I loose my fob and get my spare how does my spare then know what the code was?

It doesn't, each fob has an independent sequence.

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