Maybe two Prius in family

There is a topic in the Prius Main Forum called "lost my smart key fob in the car" that my have some information you can use even though yours is not SKS. I think the answer is no because there is some kind of complex algorithm that is unique to each car, so once the fob is programmed it can only work with one car.

 

I disagree. One fob I believe can be registered by more than one vehicle. It is the car that registers the fob, and not the other way around. I believe a non SKS car can register an SKS fob, and an SKS car can register a non-SKS fob, though of course the SKS feature would could not be registered, and would not work with that pairing.

The only way you might come to a problem is if the 'common' fob was away from one vehicle for more than say 255 executions, after which the car and fob would be out of sync, thus requiring to be re-registered as if it were a new fob.

The fobs generate a psudo-random code sequence, who's next code can be predicted by a complex algorithm, assuming the last code was known. If a code send by the fob was missed by the car, when it received the subsequent code, it sees if it matches one of the next 255 codes it would expect to get from the last one it accepted. This is also how a rolling code garage door system works.

 

I see one issue if this does work. if you have one fob and the battery dies you only have one normal key and a 50/50 chance of being in the correct car for the key to unlock it.

 

That's a good point. Make a copy of the mechanical key and store it somewhere, or get a credit card key made.