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Comment by didgetmaster | Hacker News Reader

The xkcd reminds me of a friend who was locked out of her car. The battery in her remote key fob had run down so the door would not unlock when she pushed the unlock button on it. She was still trying to figure out online how to get a new battery when I took her key from her and opened the door by inserting it in the lock. She was so embarrassed that she wouldn't talk to me for a few days.

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I’m fairly certain we’ve recently fought to open a rented car because the keyfob died and the way to extract the key from the fob was non-obvious.

Then when we finally got inside, the car didn’t have a keyhole to start it at all. Ended up calling the rental agency that showed us how to invoke the magic sequence by holding the (empty) fob in front of the start button for a few seconds before pressing it. I guess it does passive RFiD or something?

Anyway, that’s the point where I decided modern cars are not my thing.

That's the immobilizer chip. It's a little pill-shaped RFID-like thing that's been inside keys since long before remote locks and push-to-start. Basically any key that has some plastic instead of being entirely metal. The reader is located immediately next to the ignition key hole on the steering column, and that location is sometimes used even in push-to-start cars although apparently in your case it was near the start button instead. Distance is limited to a couple centimeters max. Car won't start unless the immobilizer's reader sees the correct key. When a push-to-start fob's battery is in working order, the distance is moot because it uses full blown RF instead.

Modern is a subjective thing. I have a golf 5 from 2005 (tdi). One day I had to go somewhere and it turns out the car starts and shuts itself down immediately... It turns out the ground connection to the dash was intermittent. The dash for some unknown reason is the place where the immobiliser code/certificate is stored so when you start the car the Ecu has to talk to both the immobiliser coil next to the key and the dash.

I'll leave it to readers imagination how long it took me to troubleshoot the issue.

I did that, recently. My fob battery died, I unlocked the car with the key, opened the door and... the car alarm went off. I'm not sure what the designers were thinking.

You turn the alarm off by starting the car, because the ignition has an rfid-like close-range reader which only requires passive circuitry in the key. That's how you differentiate between a break-in and the legitimate owner.

My car has push start (like many new ones) & has no keyhole inside (it has one in door to open the door). Although it has a seat/slot for the whole key to go in, in case of low battery. I assume that will stop the alarm. :-|

My car is also push start and I have to hold the fob in front of the start button for a short while before turning on the car if the fob battery is out.

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