sarah graiman's hand...

[pheonix_knight]

in the pilot episode we are lead to believe that Charles and Sarah are somewhat estranged from each other but not only did she know how to reactivate KI3T by putting her hand on the screen, her handprint must have been recorded on there so that she could do that if needed to...

go figure...???

[KarlKnightRider]

I'd say there's a pretty reasonable explanation for this. I don't believe it had been very long that Sarah and her father weren't speaking. Only a few years. Remember KITT is just another computer, and as was mentioned in the pilot she collaborated a lot with her father. When making computer systems etc, Sarah would've probably had her hand print inserted then, and used the same method to get into other systems. Doing so with KITT would've just been natural for her to do so.

[whet]

Also, whatever diffrences Charles was having with Sara, she is still his daughter, so he would plan for the possablilty that Sara might have to re activate Kitt for some reason.

Don't forget he had proggrammed Kitt to go and get Sara and ensure her safety it's unlikley he's overlook her being able to reactivate Kitt.