Once in a while, the theft protection system won't recognize the key. Have to take it in and out of the ignition a few times before it starts. The trick is you have to turn the battery on (turn it one position), look for the light on the dash with the yellow car with a key inside it, if you don't see that light you'll just waste the battery turning over the engine. It always picks the worst time too, usually when someone else is in my car and I've just finished bragging about how reliable it is! One time it would not start at all, was sitting in the parking lot for 20 minutes fighting with it, the yellow light would not turn on, which meant the engine wouldn't either! Had the car towed to the Hyundai dealership, of course when the technician went to try it the engine started first try, that was embarrassing... I asked them to fix it and they said it would be like "finding a needle in a haystack" and told me it was not worth it as it was only happening occasionally, so I had them cut me a new key (costed $125, what a rip!), that did not help at all.