Hi - we just became a 2-Prius family with the addition today of a used 2005 prius to our existing 2006 model. Since the used Prius only came with a single key, I was researching into additional SKS fobs... when I came up with the question as to whether our existing 2006 fobs could ALSO be programmed into the 2005 car? I.e. could we use our existing keys to open/start both cars? Has anyone tried this? It would seem that since the car is programmed to accept the fob, and the fob itself isn't programmed, this should be possible. Of course, the metal key stored in the fob would only open 1 of the cars, but that could easily be remedied through the "magnetic spare key" idea I've seen posted numerous times.
There was a thread posted just a few days ago asking the same thing. Search for the thread. The short answer is NO.
The fobs use a rolling code. Each time a fob is used with a car the code jumps to the next value. The long and the short of it is that the fob gets out of sequence with the other car. In theory you could make this work if you resynchronized each time, but in practice no one has made it work. A two car fob would be a nice option, just in case Toyota is reading this post. Tom