One of my two key cards failed. So I'll get another next time I'm at the service center. As for devaluating a lost card, my Prius and BMW 'memorized' the RFI number of the valid cards. I suspect Tesla can invalidate them over-the-air. But there is the optional "PIN to drive."Not really related, but as I understand it, my cell phone acts as my car key. Also, there are credit card sized cards that can be used. If you lose one of those cards, say in the garage at work, and you want to do the equivalent of re-keying the car in case someone finds that card, how big a deal is that and how expensive is it?